Touch screen for privacy display

ABSTRACT

A display comprises a polarised output spatial light modulator, switchable liquid crystal retarder, absorbing polariser and touch panel electrodes. The electrodes of the switchable liquid crystal retarder shield the touch panel electrodes from the electrical noise of the spatial light modulator addressing. The touch panel control and sensing may be synchronised with the driving signal of the switchable liquid crystal retarder. The touch panel may be operated independently of the timing of the data addressing of the spatial light modulator.

TECHNICAL FIELD

This disclosure generally relates to touch input for display deviceswith control of angular illumination for use in privacy display and lowstray light displays.

BACKGROUND

Privacy displays provide image visibility to a primary user (that istypically in an on-axis position) and reduced visibility of imagecontent to a snooper, that is typically in an off-axis position. Aprivacy function may be provided by micro-louvre optical films thattransmit a higher luminance from a display in an on-axis direction withlower luminance in off-axis positions, however such films are notelectrically switchable, and thus the display is limited to privacy onlyfunction.

Switchable privacy displays may be provided by control of the off-axisoptical output.

Control of off-axis privacy may be provided by means of contrastreduction, for example by adjusting the liquid crystal out-of-plane tiltin an In-Plane-Switching LCD.

Control may be further provided by means of off-axis luminancereduction. Luminance reduction may be achieved by means of switchablebacklights for a liquid crystal display (LCD) spatial light modulator(SLM). Off-axis luminance reduction may also be provided by switchableliquid crystal retarders, polarisers and compensation retarders arrangedto modulate the input and/or output directional luminance profile of aSLM.

Touch screens are arranged to receive input locations from observerfingers or a stylus and may comprise capacitive touch, resistive touch,electro-magnetic resonance and other known touch sensing technologies.

BRIEF SUMMARY

According to a first aspect of the present disclosure, there is provideda touch input display device comprising: a spatial light modulator (SLM)arranged to output light; a display polariser arranged on the outputside of the SLM, wherein the display polariser is a linear polariser; anadditional polariser arranged on the output side of the displaypolariser, wherein the additional polariser is a linear polariser; aswitchable liquid crystal retarder comprising a layer of liquid crystalmaterial arranged between the display polariser and the additionalpolariser, wherein the switchable liquid crystal retarder is a polarcontrol retarder that is arranged, in a switchable state of theswitchable liquid crystal retarder, simultaneously to introduce no netrelative phase shift to orthogonal polarisation components of lightpassed by the display polariser along an axis along a normal to theplane of the switchable liquid crystal retarder and introducing arelative phase shift to orthogonal polarisation components of lightpassed by the display polariser along an axis inclined to a normal tothe plane of the switchable liquid crystal retarder; switchable retardercontrol electrodes arranged to apply a voltage for controlling the stateof the switchable liquid crystal retarder; and at least one touchelectrode array arranged in a layer on the output side of the switchableretarder control electrodes. Advantageously touch sensing may beprovided for a switchable directional display that may have a first modethat has high contrast and luminance for a wide range of viewingpositions and with a second mode that has high contrast and luminancefor a head-on user and low luminance for off-axis viewing positions.Such a display may provide a switchable privacy operation or may provideswitchable stray light for example for use in night time operation.

The touch input display device may further comprise at least one passiveretarder arranged between the switchable liquid crystal retarder and theadditional polariser. The at least one passive retarder may be a polarcontrol retarder that simultaneously introduces no net relative phaseshift to orthogonal polarisation components of light passed by thedisplay polariser along an axis along a normal to the plane of theswitchable liquid crystal retarder and introducing a relative phaseshift to orthogonal polarisation components of light passed by thedisplay polariser along an axis inclined to a normal to the plane of theswitchable liquid crystal retarder. Advantageously the polar angularrange for which high image visibility is achieved in the first mode maybe increased and the polar angular range for which high visual securitylevels are achieved in the second mode may be increased.

The touch electrode array in the case that the display device comprisesone touch electrode array, or one of the touch electrode arrays in thecase that in the case that the display device comprises more than onetouch electrode array, may be formed on a surface of the passiveretarder in the case that the display device comprises one passiveretarder or on a surface of one of the passive retarders in the casethat the display device comprises more than one passive retarder. Thetouch sensing structure may be formed in a single electrode conductordeposition process and add little or no thickness to the directionaldisplay and advantageously may have low cost.

The at least one touch electrode array may comprise a pair of touchelectrode arrays arranged in layers separated by at least one dielectriclayer. Advantageously the electrode routing topology may be simplifiedin comparison to the pair of touch electrodes arranged in a singlelayer, reducing complexity and improving accuracy performance the touchelectrode arrays.

Each of the pair of touch electrode arrays may be formed on a respectivesurface of the passive retarder in the case that the display devicecomprises one passive retarder or a respective surface of one of thepassive retarders in the case that the display device comprises morethan one passive retarder. Advantageously low cost fabrication methodsmay be provided for forming the electrode arrays. The passive retardersmay be flexible for curved, bendable and foldable displays. Little or noadded thickness is provided and cost is minimised.

Said at least one dielectric layer may comprise the passive retarder inthe case that the display device comprises one passive retarder orcomprises at least one of the passive retarders in the case that thedisplay device comprises more than one passive retarder. The number oflayers is reduced, advantageously reducing thickness, complexity andcost.

The display device may comprise more than one passive retarder and saidat least one dielectric layer may comprise at least two passiveretarders. The passive retarder may be formed conveniently on A-plateretarders, advantageously reducing cost. Further the passive retardersmay be provided by materials which are suitable for forming electrodesthereon.

Said at least one dielectric layer may comprise at least one additionallayer that is not a retarder. Advantageously the dielectric layer may beadjusted to provide appropriate electrical properties independently ofthe selection of retarder materials and thicknesses.

The at least one passive retarder may comprise a passive uniaxialretarder having an optical axis perpendicular to the plane of thepassive uniaxial retarder. The number of retarders may be reduced,advantageously reducing thickness.

The at least one passive retarder may comprise a pair of passiveuniaxial retarders having optical axes in the plane of the passiveuniaxial retarders that are crossed. Electrode arrays may be formed onone side of each of the retarders, reducing the complexity of electrodeformation. Advantageously fabrication cost may be reduced.

The at least one touch electrode array may comprise a pair of touchelectrode arrays formed on facing surfaces of respective ones of thepair of passive uniaxial retarders, and said at least one dielectriclayer may comprise at least one additional layer arranged between thepair of passive uniaxial retarders. Said at least one dielectric layermay comprise an adhesive layer arranged between the pair of touchelectrode arrays. Advantageously a low cost structure may be provided.The dielectric properties may be selected by selection of the additionallayer material and thickness to achieve improved sensitivity of touchsensing.

The at least one touch electrode array may comprise a pair of touchelectrode arrays formed on outer surfaces of respective ones of the pairof passive uniaxial retarders, and said at least one dielectric layermay comprise the pair of passive uniaxial retarders. The pair ofretarders may be solvent bonded advantageously reducing surfacereflections and thickness.

The touch input display device may further comprise input and outputtransparent support substrates, the layer of liquid crystal materialbeing arranged between the input and output transparent supportsubstrates, and the at least one touch electrode array being arranged onthe output side of the output transparent support substrate. The touchinput display device may further comprise input and output transparentsupport substrates, the layer of liquid crystal material being arrangedbetween the input and output transparent support substrates, and the atleast one touch electrode array being arranged between the switchableretarder control electrodes and the output transparent supportsubstrate. The touch sensing structure may be shielded from the controlof the SLM advantageously increasing sensitivity.

The at least one touch electrode arrays may be arranged between theswitchable retarder control electrodes and the additional polariser.Advantageously the visibility of reflections from the touch electrodearrays may be reduced. Further the touch electrode arrays may beintegrated with the retarder structure, advantageously reducingthickness and cost.

The at least one touch electrode array may be separated from theswitchable retarder control electrodes. The switchable retarder controlelectrodes may be arranged on both sides of the layer of liquid crystalmaterial. Advantageously the switchable retarder may be switchedindependently of the control of the touch electrode arrays.

The touch input display device may further comprise a control system,wherein the control system may be arranged to apply a drive voltage tothe switchable retarder control electrodes for controlling theswitchable liquid crystal retarder, and the control system may bearranged to address the at least one touch electrode array forcapacitive touch sensing. Advantageously control of a switchabledirectional display and touch control can be achieved in the samedevice.

The drive voltage may have a waveform including periods where the drivevoltage is constant, and the control system may be arranged to addressthe at least one touch electrode array during at least one of theperiods where the drive voltage is constant. Advantageously the signalto noise ratio of the touch signal is greater and the sensitivity of thetouch system is improved.

The drive voltage may have a waveform including periods where the drivevoltage is constant but of respectively different levels, and thecontrol system may be arranged to address the at least one touchelectrode array during at least one of the periods where the drivevoltage is constant and at the same level. The signal to noise ratio ofthe touch signal is increased, and advantageously the sensitivity of thetouch system is improved.

The waveform of the drive voltage may include a positive addressingphase including at least one pulse of positive polarity and a negativeaddressing phase including at least one pulse of negative polarity, thepeaks of the at least one pulse of positive polarity and the peaks ofthe at least one pulse of negative polarity being said periods where thedrive voltage is constant. The average voltage across the switchableliquid crystal retarder is maintained at zero, i.e. no net DC voltageacross the switchable liquid crystal retarder, and the number ofsampling periods in which the touch signal is acquired is increased.Advantageously the lag and accuracy of the touch position determinationis improved.

The waveform of the drive voltage may include a positive addressingphase including at least one pulse of positive polarity and at least oneadditional period and a negative addressing phase including at least onepulse of negative polarity and at least one additional period, the atleast one additional period of the positive addressing phase and the atleast one additional period of the negative addressing phase being saidperiods where the drive voltage is constant and has a level intermediatethe maximum level of the at least one pulse of positive polarity and theminimum level of the at least one pulse of negative polarity. The numberof sampling periods is increased and the common mode voltage range inthe touch signal processing circuit is reduced. Advantageously the costand performance of the touch signal processing circuit is improved.

The at least one additional period of the positive addressing phase andthe at least one additional period of the negative addressing phase mayhave a level of zero volts. The number of sampling periods is increasedand the common mode voltage range in the touch signal processing circuitis further reduced. Advantageously the cost and performance of the touchsignal processing circuit is improved.

The at least one additional period of the positive addressing phase andthe at least one additional period of the negative addressing phase mayhave a level of non-zero magnitude. The number of sampling periods isincreased and the common mode voltage range in the touch signalprocessing circuit is reduced. Advantageously the touch signal positionlag is reduced and the cost of the touch signal processing circuit isimproved.

The drive voltage may have a waveform having a root mean square valuethat provides a constant liquid crystal optical alignment state of theliquid crystal retarder and having arithmetic average of zero. There isno average net DC voltage across the liquid crystal retarder. The liquidcrystal material does not degrade electrochemically, and advantageouslythe operating lifetime of the liquid crystal material is improved.

The control system may be further arranged to address the SLM. Theintegration of the control systems advantageously saves cost andcomplexity.

The drive voltage that the control system is arranged to apply to theswitchable retarder control electrodes may be synchronised with respectto the addressing of the SLM. The relative timing of the electric fieldsproduced by the electrodes of the switchable liquid crystal retarder andSLM is fixed. Advantageously any appearance of screen artefactsincluding but not limited to a “slow scanning bar” is reduced.

The control system may be arranged to address the SLM using anaddressing scheme including a vertical blanking interval, and thecontrol system being arranged to address the at least one touchelectrode array during the vertical blanking interval. During thevertical blanking interval reduced high frequency signal transitions onthe drive electrode to the SLM are achieved. The electrical fieldradiation from those transitions is reduced and advantageously the touchsensitivity of the screen is improved.

The waveform of the drive voltage may comprise an addressing sequencecomprising a first addressing positive voltage phase with a positivemaximum voltage; and a second addressing negative voltage phase with anegative minimum voltage. The waveform of the drive voltage in the firstphase may comprise more than one positive voltage level; and thewaveform of the drive voltage in the second phase may comprise more thanone negative voltage level; or the waveform of the drive voltage in thefirst phase may comprise at least one positive voltage level and a zerovoltage level; and the waveform of the drive voltage in the second phasemay comprise at least one negative voltage level and a zero voltagelevel. The touch input display device may further comprise a thirdaddressing phase comprising an intermediate drive voltage levelintermediate the positive maximum voltage and negative minimum voltage.The intermediate voltage level may be zero. The root mean square valueof the waveform of the drive voltage may be arranged to provide aconstant liquid crystal optical alignment state of the liquid crystalretarder; and wherein the arithmetic average of the waveform of thedrive voltage may be zero. The signal applied to and measured from thetouch electrode arrays may be provided when the drive voltage is at aconstant level. The switchable liquid crystal retarder may be DCbalanced so that lifetime of operation of the retarder is extended.Advantageously noise in the touch measurement system is reduced andimproved accuracy may be achieved.

The signal applied to and measured from the touch electrode arrays maybe provided when the drive voltage is at the same constant level.Advantageously the cost and complexity of the touch sensing apparatusmay be improved.

The waveform applied to the switchable liquid crystal retarder may besynchronised with respect to the addressing of the SLM. The addressingof the SLM may comprise a vertical blanking interval and the signalapplied to and measured from the touch electrode arrays is providedduring the vertical blanking interval. Advantageously electrical noisefrom the SLM in the touch signal detector is minimised and accuracy andspeed of touch measurement increased.

The touch input display device may further comprise a control system,wherein the control system may be arranged to apply a drive voltage tothe switchable retarder control electrodes for controlling theswitchable liquid crystal retarder, and the control system may bearranged to address the at least one touch electrode array forcapacitive touch sensing. Advantageously interference between the touchelectrode arrays and switchable retarder control electrodes may bereduced.

The drive voltage may have a waveform including periods where the drivevoltage is constant, and the control system may be arranged to addressthe at least one touch electrode array during at least one of theperiods where the drive voltage is constant. The drive voltage may havea waveform including periods where the drive voltage is constant but ofrespectively different levels, and the control system may be arranged toaddress the at least one touch electrode array during at least one ofthe periods where the drive voltage is constant and at the same level.The waveform of the drive voltage may include a positive addressingphase including at least one pulse of positive polarity and a negativeaddressing phase including at least one pulse of negative polarity, thepeaks of the at least one pulse of positive polarity and the peaks ofthe at least one pulse of negative polarity being said periods where thedrive voltage is constant.

The waveform of the drive voltage may include a positive addressingphase including at least one pulse of positive polarity and at least oneadditional period and a negative addressing phase including at least onepulse of negative polarity and at least one additional period, the atleast one additional period of the positive addressing phase and the atleast one additional period of the negative addressing phase being saidperiods where the drive voltage is constant and has a level intermediatethe maximum level of the at least one pulse of positive polarity and theminimum level of the at least one pulse of negative polarity.

The at least one additional period of the positive addressing phase andthe at least one additional period of the negative addressing phase mayhave a level of zero volts. The at least one additional period of thepositive addressing phase and the at least one additional period of thenegative addressing phase may have a level of non-zero magnitude. Thedrive voltage may have a waveform having a root mean square value thatprovides a constant liquid crystal optical alignment state of the liquidcrystal retarder and having arithmetic average of zero. The controlsystem may be further arranged to address the SLM. The drive voltagethat the control system is arranged to apply to the switchable retardercontrol electrodes may be synchronised with respect to the addressing ofthe SLM. The control system may be arranged to address the SLM using anaddressing scheme including a vertical blanking interval, and thecontrol system being arranged to address the at least one touchelectrode array during the vertical blanking interval.

The touch input display device may further comprise a reflectivepolariser arranged between the display polariser and the switchableliquid crystal retarder. Advantageously when used as a privacy displayin ambient light, increased off-axis reflectivity may be provided toachieve reduced off-image contrast to a snooper. In public mode, reducedreflectivity is achieved so that a high contrast public mode may beprovided for a wide field of view.

According to a second aspect of the present disclosure there is provideda touch input display device comprising: a SLM; a display polariserarranged on the output side of the SLM, wherein the display polariser isa linear polariser; an additional polariser arranged on the output sideof the display polariser, wherein the additional polariser is a linearpolariser; plural retarders arranged between the display polariser andthe additional polariser; wherein the plural retarders comprise: aswitchable liquid crystal retarder arranged between input and outputtransparent support substrates; and at least one passive polar controlretarder arranged between the switchable liquid crystal retarder and theadditional polariser; further comprising first and second touch inputelectrode arrays arranged between the output transparent supportsubstrate and the additional polariser.

The first and second input electrode arrays may be provided on at leastone surface of at least one passive polar control retarder. The at leastone passive polar control retarder may comprise a pair of retardersarranged in series, each passive polar control retarder comprising atouch electrode array arranged on one surface; wherein the touchelectrode arrays face each other and a dielectric material is arrangedbetween the touch electrode arrays. The pair of retarders may comprise:a pair of passive uniaxial retarders each having its optical axisperpendicular to the plane of the retarder; or a pair of passiveuniaxial retarders having optical axes in the plane of the retardersthat are crossed. The dielectric material may comprise an adhesivematerial.

The touch input display device may further comprise a control system;wherein the control system may be arranged to control the drive voltageapplied to the switchable liquid crystal retarder; and to control thesignal applied to and measured from the touch electrode arrays.Advantageously a touch location measurement may be provided with lowthickness, low cost, high accuracy and high speed.

According to a second aspect of the present disclosure, there isprovided a method of controlling a touch input display devicecomprising: a SLM arranged to output light; a display polariser arrangedon the output side of the SLM; an additional polariser arranged on theoutput side of the display polariser; a switchable liquid crystalretarder comprising a layer of liquid crystal material arranged betweenthe display polariser and the additional polariser; at least one passiveretarder arranged between the switchable liquid crystal retarder and theadditional polariser; switchable retarder control electrodes arranged toapply a voltage for controlling the switchable liquid crystal retarder;and at least one touch electrode array arranged in a layer on the outputside of the switchable retarder control electrodes, wherein the methodcomprises: applying a drive voltage to the switchable retarder controlelectrodes for controlling the switchable liquid crystal retarder,wherein the drive voltage has a waveform including periods where thedrive voltage is constant; and addressing the at least one touchelectrode array for capacitive touch sensing during at least one of theperiods where the drive voltage is constant. Advantageously a switchabledirectional display may be provided with touch sensing that has highsensitivity, high accuracy and low lag. Low thickness and cost may beachieved.

Embodiments of the present disclosure may be used in a variety ofoptical systems. The embodiment may include or work with a variety ofprojectors, projection systems, optical components, displays,microdisplays, computer systems, processors, self-contained projectorsystems, visual and/or audio-visual systems and electrical and/oroptical devices. Aspects of the present disclosure may be used withpractically any apparatus related to optical and electrical devices,optical systems, presentation systems or any apparatus that may containany type of optical system. Accordingly, embodiments of the presentdisclosure may be employed in optical systems, devices used in visualand/or optical presentations, visual peripherals and so on and in anumber of computing environments.

Before proceeding to the disclosed embodiments in detail, it should beunderstood that the disclosure is not limited in its application orcreation to the details of the particular arrangements shown, becausethe disclosure is capable of other embodiments. Moreover, aspects of thedisclosure may be set forth in different combinations and arrangementsto define embodiments unique in their own right. Also, the terminologyused herein is for the purpose of description and not of limitation.

Directional backlights offer control over the illumination emanatingfrom substantially the entire output surface controlled typicallythrough modulation of independent LED light sources arranged at theinput aperture side of an optical waveguide. Controlling the emittedlight directional distribution can achieve single person viewing for asecurity function, where the display can only be seen by a single viewerfrom a limited range of angles; high electrical efficiency, whereillumination is primarily provided over a small angular directionaldistribution; alternating left and right eye viewing for time sequentialstereoscopic and autostereoscopic display; and low cost.

These and other advantages and features of the present disclosure willbecome apparent to those of ordinary skill in the art upon reading thisdisclosure in its entirety.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example in the accompanyingFIGURES, in which like reference numbers indicate similar parts, and inwhich:

FIG. 1A is a diagram illustrating in perspective side view a touch inputdisplay device comprising a SLM, reflective polariser and switchableliquid crystal retarder wherein touch electrode arrays are provided onfacing surfaces of first and second passive polar control retarders;

FIG. 1B is a diagram illustrating in front view alignment of opticallayers and electrode layers in the optical stack of FIG. 1A;

FIG. 2A and FIG. 2B are diagrams illustrating in a different perspectiveside view the touch input display device of FIG. 1A in privacy andpublic modes respectively;

FIG. 3A is a graph illustrating the variation of output luminance withpolar direction for transmitted light rays in FIG. 1A in a privacy mode;

FIG. 3B is a graph illustrating the variation in reflectivity with polardirection for reflected light rays in FIG. 1A in a privacy mode;

FIG. 3C is a graph illustrating the variation of output luminance withpolar direction for transmitted light rays in FIG. 1A in a public mode;

FIG. 3D is a graph illustrating the variation in reflectivity with polardirection for reflected light rays in FIG. 1A in a public mode;

FIG. 4A is a diagram illustrating in front perspective view observationof reflected ambient light from interface surfaces of a display of FIG.1A in public mode;

FIG. 4B is a diagram illustrating in front perspective view observationof reflected ambient light for the display of FIG. 1A in privacy mode;

FIG. 4C is a diagram illustrating in side view an automotive vehiclewith a switchable directional display arranged within the vehicle cabinfor both entertainment and sharing modes;

FIG. 4D is a diagram illustrating in top view an automotive vehicle witha switchable directional display arranged within the vehicle cabin in anentertainment mode;

FIG. 4E is a diagram illustrating in top view an automotive vehicle witha switchable directional display arranged within the vehicle cabin in asharing mode;

FIG. 5 is a diagram illustrating in side view the touch input displaydevice of FIG. 1A;

FIG. 6A is a diagram illustrating in perspective front view electrodesand control system for a touch input display device wherein theelectrodes are arranged on opposite sides of a dielectric layer;

FIG. 6B is a diagram illustrating in perspective front view electrodesfor a touch input display device wherein the electrodes are arranged onthe same side of a dielectric layer;

FIG. 6C is a diagram illustrating in perspective front view theelectrodes of a further arrangement for a touch input display device;

FIG. 6D is a diagram illustrating in cross sectional side view anarrangement corresponding to FIG. 6C;

FIG. 7 is a diagram illustrating a circuit diagram for control of atouch input device;

FIG. 8 is a diagram illustrating in perspective front view driving of aswitchable liquid crystal retarder with voltage waveforms;

FIG. 9A is a graph illustrating driving waveforms for driving of aswitchable liquid electrode;

FIG. 9B is a graph illustrating driving waveforms for driving of aswitchable liquid crystal retarder comprising two anti-phase drivenelectrodes;

FIG. 10 is a graph illustrating a resultant voltage waveform providedacross the liquid crystal retarder for the driving waveforms of FIGS.9A-B and touch control signal;

FIG. 11A, FIG. 11B, FIG. 11C, and FIG. 11D are graphs each illustratinga resultant voltage waveform provided across the liquid crystal retarderand corresponding timing of a control signal for application to andmeasurement from the touch electrode arrays;

FIG. 12A is a graph illustrating driving waveforms for driving of aswitchable liquid crystal retarder comprising a zero volt drivenelectrode and an alternating voltage waveform driven electrode;

FIG. 12B is a graph illustrating a resultant voltage waveform providedacross the liquid crystal retarder for the driving waveforms of FIG.12A;

FIG. 13A and FIG. 13B are graphs illustrating resultant voltagewaveforms provided across the liquid crystal retarder with three andfour drive voltage levels respectively;

FIG. 14 is a graph illustrating a resultant voltage waveform providedacross the liquid crystal retarder, corresponding timing of a controlsignal for application to and measurement from the touch electrodearrays, and synchronisation with the vertical blanking interval of theSLM;

FIG. 15 is a graph illustrating a resultant voltage waveform providedacross the liquid crystal retarder, corresponding timing of a controlsignal for application to and measurement from the touch electrodearrays, asynchronously with the driving of the SLM;

FIG. 16A is a diagram illustrating in side view a touch input displaydevice wherein the dielectric layer is provided by a pair of crossedA-plates;

FIG. 16B is a diagram illustrating in perspective side view a touchinput display device wherein the dielectric layer is provided by a pairof crossed A-plates;

FIG. 16C is a diagram illustrating in perspective side view a touchinput display device wherein the dielectric layer is provided by one ofa pair of crossed A-plates;

FIG. 17 is a diagram illustrating in a perspective side view a touchinput display device wherein the dielectric layer is provided betweentwo C-plates;

FIG. 18A is a diagram illustrating in a perspective side view a touchinput display device wherein the dielectric layer is provided by aC-plate;

FIG. 18B is a diagram illustrating in side view the touch input displaydevice of FIG. 18A;

FIG. 19A is a diagram illustrating in a perspective side view a touchinput non-switchable privacy display device wherein the dielectric layeris provided between two A-plates;

FIG. 19B is a graph illustrating the variation of output transmission ofthe plural passive polar control retarders with polar direction fortransmitted light rays in FIG. 19A;

FIG. 20 is a diagram illustrating in side view a touch input displaydevice wherein the dielectric layer between the touch electrode arraysis provided between a passive retarder and the output surface of theswitchable liquid crystal retarder;

FIG. 21A is a diagram illustrating in side view a touch input displaydevice wherein the dielectric layer between the touch electrode arraysis provided by the output transparent support substrate and an adhesivelayer;

FIG. 21B is a diagram illustrating in side view a touch input displaydevice wherein the touch electrode arrays are provided between one ofthe liquid crystal control electrodes and the output transparent supportsubstrate of the switchable liquid crystal retarder;

FIG. 21C is a diagram illustrating in a perspective side view a touchinput display device wherein the dielectric layer between the touchelectrode arrays is provided by the output transparent support substrateof the switchable liquid crystal retarder;

FIG. 22 is a diagram illustrating in a perspective side view a touchinput switchable privacy display device wherein the touch electrodearrays are arranged between the liquid crystal polar control retarderand additional polariser;

FIG. 23A is a diagram illustrating in perspective view illumination of aretarder layer by off-axis light;

FIG. 23B is a diagram illustrating in perspective view illumination of aretarder layer by off-axis light of a first linear polarization state at0 degrees;

FIG. 23C is a diagram illustrating in perspective view illumination of aretarder layer by off-axis light of a first linear polarization state at90 degrees;

FIG. 23D is a diagram illustrating in perspective view illumination of aretarder layer by off-axis light of a first linear polarization state at45 degrees;

FIG. 24A is a diagram illustrating in perspective view illumination of aC-plate retarder by off-axis polarised light with a positive elevation;

FIG. 24B is a diagram illustrating in perspective view illumination of aC-plate retarder by off-axis polarised light with a negative lateralangle;

FIG. 24C is a diagram illustrating in perspective view illumination of aC-plate retarder by off-axis polarised light with a positive elevationand negative lateral angle;

FIG. 24D is a diagram illustrating in perspective view illumination of aC-plate retarder by off-axis polarised light with a positive elevationand positive lateral angle;

FIG. 24E is a graph illustrating the variation of output transmissionwith polar direction for transmitted light rays in FIGS. 24A-D;

FIG. 25A is a diagram illustrating in perspective view illumination ofcrossed A-plate retarder layers by off-axis polarised light with apositive elevation;

FIG. 25B is a diagram illustrating in perspective view illumination ofcrossed A-plate retarder layers by off-axis polarised light with anegative lateral angle;

FIG. 25C is a diagram illustrating in perspective view illumination ofcrossed A-plate retarder layers by off-axis polarised light with apositive elevation and negative lateral angle;

FIG. 25D is a diagram illustrating in perspective view illumination ofcrossed A-plate retarder layers by off-axis polarised light with apositive elevation and positive lateral angle; and

FIG. 25E is a graph illustrating the variation of output transmissionwith polar direction for transmitted light rays in FIGS. 25A-D.

DETAILED DESCRIPTION

Terms related to optical retarders for the purposes of the presentdisclosure will now be described.

In a layer comprising a uniaxial birefringent material there is adirection governing the optical anisotropy whereas all directionsperpendicular to it (or at a given angle to it) have equivalentbirefringence.

The optical axis of an optical retarder refers to the direction ofpropagation of a light ray in the uniaxial birefringent material inwhich no birefringence is experienced. This is different from theoptical axis of an optical system which may for example be parallel to aline of symmetry or normal to a display surface along which a principalray propagates.

For light propagating in a direction orthogonal to the optical axis, theoptical axis is the slow axis when linearly polarized light with anelectric vector direction parallel to the slow axis travels at theslowest speed. The slow axis direction is the direction with the highestrefractive index at the design wavelength. Similarly the fast axisdirection is the direction with the lowest refractive index at thedesign wavelength.

For positive dielectric anisotropy uniaxial birefringent materials theslow axis direction is the extraordinary axis of the birefringentmaterial. For negative dielectric anisotropy uniaxial birefringentmaterials the fast axis direction is the extraordinary axis of thebirefringent material.

The terms half a wavelength and quarter a wavelength refer to theoperation of a retarder for a design wavelength λ₀ that may typically bebetween 500 nm and 570 nm. In the present illustrative embodimentsexemplary retardance values are provided for a wavelength of 550 nmunless otherwise specified.

The retarder provides a relative phase shift between two orthogonalpolarization components of the light wave incident thereon and ischaracterized by the amount of relative phase, F, that it imparts on thetwo polarization components. In some contexts, the term “phase shift” isused without the word “relative” but still meaning relative phase shift.The relative phase shift is related to the birefringence Δn and thethickness d of the retarder by:Γ=2·π·Δn·d/λ ₀  eqn. 1

In eqn. 1, Δn is defined as the difference between the extraordinary andthe ordinary index of refraction, i.e.Δn=n _(e) −n _(o)  eqn. 2

For a half-wave retarder, the relationship between d, Δn, and λ₀ ischosen so that the phase shift between polarization components is Γ=π.For a quarter-wave retarder, the relationship between d, Δn, and λ₀ ischosen so that the phase shift between polarization components is Γ=π/2.

The term half-wave retarder herein typically refers to light propagatingnormal to the retarder and normal to the spatial light modulator (SLM).

Some aspects of the propagation of light rays through a transparentretarder between a pair of polarisers will now be described.

The state of polarisation (SOP) of a light ray is described by therelative amplitude and phase shift between any two orthogonalpolarization components. Transparent retarders do not alter the relativeamplitudes of these orthogonal polarisation components but act only ontheir relative phase. Providing a net phase shift between the orthogonalpolarisation components alters the SOP whereas maintaining net relativephase preserves the SOP.

A linear SOP has a polarisation component with a non-zero amplitude andan orthogonal polarisation component which has zero amplitude.

A linear polariser transmits a unique linear SOP that has a linearpolarisation component parallel to the electric vector transmissiondirection of the linear polariser and attenuates light with a differentSOP.

Absorbing polarisers are polarisers that absorb one polarisationcomponent of incident light and transmit a second orthogonalpolarisation component. Examples of absorbing linear polarisers aredichroic polarisers.

Reflective polarisers are polarisers that reflect one polarisationcomponent of incident light and transmit a second orthogonalpolarisation component. Examples of reflective linear polarisers aremultilayer polymeric film stacks such as DBEF™ or APF™ from 3MCorporation, or wire grid polarisers such as ProFlux™ from Moxtek.

A retarder arranged between a linear polariser and a parallel linearanalysing polariser that introduces no relative net phase shift providesfull transmission of the light other than residual absorption within thelinear polariser.

A retarder that provides a relative net phase shift between orthogonalpolarisation components changes the SOP and provides attenuation at theanalysing polariser.

In the present disclosure an ‘A-plate’ refers to an optical retarderutilizing a layer of birefringent material with its optical axisparallel to the plane of the layer.

A ‘positive A-plate’ refers to positively birefringent A-plates, i.e.A-plates with a positive Δn.

In the present disclosure a ‘C-plate’ refers to an optical retarderutilizing a layer of birefringent material with its optical axisperpendicular to the plane of the layer. A ‘positive C-plate’ refers topositively birefringent C-plate, i.e. a C-plate with a positive Δn. A‘negative C-plate’ refers to a negatively birefringent C-plate, i.e. aC-plate with a negative Δn.

‘O-plate’ refers to an optical retarder utilizing a layer ofbirefringent material with its optical axis having a component parallelto the plane of the layer and a component perpendicular to the plane ofthe layer. A ‘positive O-plate’ refers to positively birefringentO-plates, i.e. O-plates with a positive Δn.

Achromatic retarders may be provided wherein the material of theretarder is provided with a retardance Δn·d that varies with wavelengthλ asΔn·d/λ=κ  eqn. 3

where κ is substantially a constant.

Examples of suitable materials include modified polycarbonates fromTeijin Films. Achromatic retarders may be provided in the presentembodiments to advantageously minimise colour changes between polarangular viewing directions which have low luminance reduction and polarangular viewing directions which have increased luminance reductions aswill be described below.

Various other terms used in the present disclosure related to retardersand to liquid crystals will now be described.

A liquid crystal cell has a retardance given by Δn·d where Δn is thebirefringence of the liquid crystal material in the liquid crystal celland d is the thickness of the liquid crystal cell, independent of thealignment of the liquid crystal material in the liquid crystal cell.

Homogeneous alignment refers to the alignment of liquid crystals inswitchable liquid crystal displays where molecules align substantiallyparallel to a substrate. Homogeneous alignment is sometimes referred toas planar alignment. Homogeneous alignment may typically be providedwith a small pre-tilt such as 2 degrees, so that the molecules at thesurfaces of the alignment layers of the liquid crystal cell are slightlyinclined as will be described below. Pretilt is arranged to minimisedegeneracies in switching of cells.

In the present disclosure, homeotropic alignment is the state in whichrod-like liquid crystalline molecules align substantiallyperpendicularly to the substrate. In discotic liquid crystalshomeotropic alignment is defined as the state in which an axis of thecolumn structure, which is formed by disc-like liquid crystallinemolecules, aligns perpendicularly to a surface. In homeotropicalignment, pretilt is the tilt angle of the molecules that are close tothe alignment layer and is typically close to 90 degrees and for examplemay be 88 degrees.

In a twisted liquid crystal layer a twisted configuration (also known asa helical structure or helix) of nematic liquid crystal molecules isprovided. The twist may be achieved by means of a non-parallel alignmentof alignment layers. Further, cholesteric dopants may be added to theliquid crystal material to break degeneracy of the twist direction(clockwise or anti-clockwise) and to further control the pitch of thetwist in the relaxed (typically undriven) state. A supertwisted liquidcrystal layer has a twist of greater than 180 degrees. A twisted nematiclayer used in SLMs typically has a twist of 90 degrees.

Liquid crystal molecules with positive dielectric anisotropy areswitched from a homogeneous alignment (such as an A-plate retarderorientation) to a homeotropic alignment (such as a C-plate or O-plateretarder orientation) by means of an applied electric field.

Liquid crystal molecules with negative dielectric anisotropy areswitched from a homeotropic alignment (such as a C-plate or O-plateretarder orientation) to a homogeneous alignment (such as an A-plateretarder orientation) by means of an applied electric field.

Rod-like molecules have a positive birefringence so that n_(e)>n_(o) asdescribed in equation 2. Discotic molecules have negative birefringenceso that n_(e)<n_(o).

Positive retarders such as A-plates, positive O-plates and positiveC-plates may typically be provided by stretched films or rod-like liquidcrystal molecules. Negative retarders such as negative C-plates may beprovided by stretched films or discotic like liquid crystal molecules.

Parallel liquid crystal cell alignment refers to the alignment directionof homogeneous alignment layers being parallel or more typicallyantiparallel. In the case of pre-tilted homeotropic alignment, thealignment layers may have components that are substantially parallel orantiparallel. Hybrid aligned liquid crystal cells may have onehomogeneous alignment layer and one homeotropic alignment layer. Twistedliquid crystal cells may be provided by alignment layers that do nothave parallel alignment, for example oriented at 90 degrees to eachother.

Transmissive SLMs may further comprise retarders between the inputdisplay polariser and the output display polariser for example asdisclosed in U.S. Pat. No. 8,237,876, which is herein incorporated byreference in its entirety. Such retarders (not shown) are in a differentplace to the passive retarders of the present embodiments. Suchretarders compensate for contrast degradations for off-axis viewinglocations, which is a different effect to the luminance reduction foroff-axis viewing positions of the present embodiments.

A private mode of operation of a display is one in which an observersees a low contrast sensitivity such that an image is not clearlyvisible. Contrast sensitivity is a measure of the ability to discernbetween luminances of different levels in a static image. Inversecontrast sensitivity may be used as a measure of visual security, inthat a high visual security level (VSL) corresponds to low imagevisibility.

For a privacy display providing an image to an observer, visual securitymay be given as:VSL=(Y+R)/(Y−K)  eqn. 4

where VSL is the visual security level, Y is the luminance of the whitestate of the display at a snooper viewing angle, K is the luminance ofthe black state of the display at the snooper viewing angle and R is theluminance of reflected light from the display.

Panel contrast ratio is given as:C=Y/K  eqn. 5

For high contrast optical LCD modes, the white state transmissionremains substantially constant with viewing angle. In the contrastreducing liquid crystal modes of the present embodiments, white statetransmission typically reduces as black state transmission increasessuch thatY+K˜P·L  eqn. 6

The visual security level may then be further given as:

$\begin{matrix}{{VSL} = \frac{\left( {C + {{I.\rho}\text{/}{\pi.\left( {C + 1} \right)}\text{/}\left( {P.L} \right)}} \right)}{\left( {C - 1} \right)}} & {{eqn}.\mspace{14mu} 7}\end{matrix}$

where off-axis relative luminance, P is typically defined as thepercentage of head-on luminance, L at the snooper angle and the displaymay have image contrast ratio C and the surface reflectivity is ρ.

The off-axis relative luminance, P is sometimes referred to as theprivacy level. However, such privacy level P describes relativeluminance of a display at a given polar angle compared to head-onluminance, and is not a measure of privacy appearance.

The display may be illuminated by Lambertian ambient illuminance I. Thusin a perfectly dark environment, a high contrast display has VSL ofapproximately 1.0. As ambient illuminance increases, the perceived imagecontrast degrades, VSL increases and a private image is perceived.

For typical liquid crystal displays the panel contrast C is above 100:1for almost all viewing angles, allowing the visual security level to beapproximated to:VSL=1+I·ρ/(π·P·L)  eqn. 8

In comparison to privacy displays, desirably wide angle displays areeasily observed in standard ambient illuminance conditions. One measureof image visibility is given by the contrast sensitivity such as theMichelson contrast which is given by:M=(I _(max) ÷I _(min))/(I _(max) +I _(min))  eqn. 9and so:M=((Y+R)−(K+R))/((Y+R)+(K+R))=(Y−K)/(Y+K+2·R)  eqn. 10

Thus the visual security level (VSL), is equivalent (but not identicalto) 1/M. In the present discussion, for a given off-axis relativeluminance, P the wide angle image visibility, W is approximated asW=1/VSL=1/(1+I·ρ/(π·P·L))  eqn. 11

It would be desirable to provide touch panel functionality for aswitchable directional display apparatus comprising a switchable liquidcrystal retarder arranged between a display output polariser and anadditional polariser for use in displays such as privacy displays andlow stray light displays such as displays for night time use.

FIG. 1A is a schematic diagram illustrating in perspective side view atouch input display device 100 comprising a spatial light modulator(SLM) 48, reflective polariser 302 and switchable liquid crystalretarder 301 wherein touch electrode arrays 500, 502 are provided onfacing surfaces of first and second passive polar control retarders330A, 330B; and FIG. 1B is a schematic diagram illustrating in frontview alignment of optical layers and electrode layers in the opticalstack of FIG. 1A.

In the present disclosure finger 25 location is detected by means of thetouch electrode arrays 500, 502 and control system 400, 450, 250, 350 aswill be described further hereinbelow.

A touch input display device 100 comprises: a SLM 48 arranged to outputlight 400; a display polariser 218 arranged on the output side of theSLM 48; an additional polariser 318 arranged on the output side of thedisplay polariser 218; a switchable liquid crystal retarder 301comprising a layer 314 of liquid crystal material 414 arranged betweenthe display polariser 218 and the additional polariser 318; passivepolar control retarders 330A, 330B arranged between the switchableliquid crystal retarder 301 and the additional polariser 318; switchableretarder control electrodes 413, 415 arranged to apply a voltage, V forcontrolling the switchable liquid crystal retarder 301; and touchelectrode arrays 500, 502 arranged in a layer on the output side ofswitchable retarder control electrodes 413, 415.

The display polariser 218, reflective polariser 302 and additionalpolariser 318 are linear polarisers with electric vector transmissiondirections 219, 303, 319 respectively.

The switchable liquid crystal retarder 301 comprises transparent supportsubstrates 312, 316. Electrodes 413, 415 and alignment layers (notshown) are arranged on the facing surfaces of support substrates 312,316 respectively in order to provide alignment and electrical control tothe layer 314 of liquid crystal material 414. The switchable retardercontrol electrodes 413, 415 are arranged on both sides of the layer 314of liquid crystal material 414.

Each of the pair of touch electrode arrays 500, 502 are formed on arespective surface of one of the passive polar control retarders 330A,330B in the case of FIGS. 1A-B that the display device comprises morethan one passive retarder. The touch electrode array 500, is formed on asurface of the passive polar control retarder 330A and the touchelectrode array 502 is formed on a surface of the passive polar controlretarder 330B.

The touch electrode arrays comprise a pair of touch electrode arrays500, 502 formed on facing surfaces of respective ones of the pair ofpassive polar control retarders that are uniaxial retarders 330A, 330Band said at least one dielectric layer 504 comprises at least oneadditional layer arranged between the pair of passive uniaxialretarders. The pair of touch electrode arrays 500, 502 are arranged inlayers separated by dielectric layer 504. The dielectric layer 504 isarranged between the switchable liquid crystal layer 314 and theadditional polariser 318. The first and second touch electrode arrays500, 502 are arranged on the dielectric layer 504 and on opposite sidesof the dielectric layer 504.

The touch electrode arrays 500, 502 are arranged between the switchableretarder control electrodes 413, 415 and the additional polariser 318and are separated from the switchable retarder control electrodes 413,415.

The touch input display device 100 further comprises a control system400, wherein the control system 400 is arranged to apply a drive voltageV to the switchable retarder control electrodes 413, 415 for controllingthe switchable liquid crystal retarder 301 by means of driver 350. Thecontrol system 400 is further arranged to address the touch electrodearrays 500, 502 for capacitive touch sensing.

Optional reflective polariser 302 is arranged between the displaypolariser 218 and the polar control retarder 300. Polar control retarder300 is arranged between the reflective polariser 302 (or outputpolariser 218 if reflective polariser 302 is omitted) and the additionalpolariser 318. The electric vector transmission direction 303 of thereflective polariser 302 is parallel to the electric vector transmissiondirection 219 of the display polariser 218 and electric vectortransmission direction 319 of the additional polariser 318.

In the embodiment of FIGS. 1A-B, the polar control retarder 300comprises passive polar control retarder 330 and switchable liquidcrystal retarder 301, but in general may be replaced by otherconfigurations of at least one retarder, some examples of which arepresent in the devices described below.

The present embodiments provide a switchable privacy display that isswitchable between a privacy mode with a wide polar region in which highvisual security level is achieved and a public mode of operation with awide polar region in which high image visibility is achieved. Theoperation of said privacy display is provided by polar control retarder300 as will now be described.

The at least one polar control retarder 300 comprises the switchableliquid crystal retarder 301 that is arranged in a switchable state ofthe switchable liquid crystal retarder 301, simultaneously to introduceno net relative phase shift to orthogonal polarisation components oflight passed by the reflective polariser 302 along an axis along anormal to the plane of the at least one polar control retarder 300 andto introduce a net relative phase shift to orthogonal polarisationcomponents of light passed by the reflective polariser 302 along an axisinclined to a normal to the plane of the at least one polar controlretarder 300.

Polar control retarder 300 further comprises at least one passive polarcontrol retarder 330 that in FIGS. 1A-B comprises a pair of passiveuniaxial retarders 330A, 330B having optical axes in the plane of thepassive uniaxial retarders that are crossed. The passive polar controlretarders 330A, 330B provide a polar control retarder 300 thatsimultaneously introduces no net relative phase shift to orthogonalpolarisation components of light passed by the display polariser 218 andreflective polariser 302 along an axis along a normal to the plane ofthe switchable liquid crystal retarder 301 and introduce a relativephase shift to orthogonal polarisation components of light passed by thedisplay polariser along an axis inclined to a normal to the plane of theswitchable liquid crystal retarder.

The polar control retarder 300 does not affect the luminance of lightpassing through the reflective polariser 302, the polar control retarder300 and the additional polariser 318 along an axis along a normal to theplane of the polar control retarder 300 but the polar control retarder300 does reduce the luminance of light passing therethrough along anaxis inclined to a normal to the plane of the polar control retarder300, at least in one of the switchable states of the switchable retarder301. The principles leading to this effect are described in greaterdetail below with reference to FIGS. 33A-35E and arises from thepresence or absence of a phase shift introduced by the polar controlretarder 300 to light along axes that are angled differently withrespect to the liquid crystal material of the polar control retarder300. A similar effect is achieved in all the devices described below.

The control system 400 is further arranged to address the SLM 48. Thecontrol system comprises a system controller 400 that is arranged to (i)provide image data to the SLM 48 by means of SLM controller 250 (ii)provide control of the voltage driver 350 to control the drive voltageapplied to the switchable liquid crystal retarder and (iii) and tocontrol the signal applied to and measured from the touch electrodearrays 500, 502 by means of touch controller 450 and touch drivers 452,454.

The operation of the polar control retarder 300 will now be furtherdescribed.

FIGS. 2A-B are schematic diagrams illustrating in a differentperspective side view the touch input display device of FIG. 1A foroperation in a privacy and public modes of operation respectively.Features of the embodiment of FIGS. 2A-B not discussed in further detailmay be assumed to correspond to the features with equivalent referencenumerals as discussed above, including any potential variations in thefeatures.

The touch electrode arrays are arranged on the facing surfaces of thepair of passive uniaxial retarders 330A, 330B. The dielectric layer 504comprises an adhesive layer provided between the touch electrode arraysarranged on the facing surfaces of the pair of passive uniaxialretarders. The dielectric layer 504 may comprise for example anoptically clear adhesive (OCA) or pressure sensitive adhesive (PSA), ormay be provided by another dielectric material.

Touching finger 25 may be near or in contact with substrate 320 that maybe a glass cover with oleophobic hard coating to achieve mechanicalrobustness and resistance to finger grease. Touch control may also beprovided by a pen or stylus.

In operation the layer 314 of liquid crystal material 414 is driven byvoltage driver 350 with a first voltage waveform Va to provide a firstliquid crystal alignment for privacy operation in FIG. 2A and is drivenby voltage driver 350 with a second voltage waveform Vb to provide asecond liquid crystal alignment for wide angle operation in FIG. 2B.

The at least one passive polar control retarder 330 comprises a pair ofretarders 330A, 330B arranged in series, each passive polar controlretarder 330A, 330B comprising touch electrode array 500 or touchelectrode array 502 arranged on one surface; wherein the touch electrodearrays 500, 502 face each other and a dielectric material 504 isarranged between the touch electrode arrays 500, 502.

Touch electrode arrays 500, 502 may comprise transparent conductors forexample ITO, silver nanowires or conductive polymers. They may be formedby know techniques including physical vapour deposition, sputtering,evaporation, ink jet printing or contact printing. They may be patternedby the use of masks or photo resists and etching. When the electrodesare formed on the flexible retarder substrates, for example PC orCOC/COP, then the type and temperature of the electrode depositionprocess may be controlled to avoid melting or the substrate. Inherentlylow temperature processes such as ink jet and contact printing canproduce electrode layers without exceeding the glass transitiontemperature of the substrates.

The topology of routing of the touch electrode arrays 500, 502 formed onseparate substrates may have more options and be simpler than therouting topology if the electrodes are provided on a single surface of aretarder. When formed as a single layer the two electrodes arrays cannothave crossing electrode traces (without extra processing steps to addintermediate insulating bridges or an intermediate dielectric layer).For example intermediate dielectric layers may be provided betweenlayers of the electrode layers 500, 502 if the electrode arrays 500, 502are formed on a single surface. The fabrication of such arrays requiresalignment during the electrode array formation process increasing cost.Advantageously the cost of electrode array 500, 502 formation may bereduced when the electrode arrays 500, 502 are formed on differentsubstrates that are the retarders 300A, 300B.

The visual appearance of an illustrative embodiment similar to thatshown in FIGS. 2A-B will now be described.

FIG. 3A is a schematic graph illustrating the variation of outputluminance with polar direction for transmitted light rays in FIG. 1A andFIG. 2A in a privacy mode of operation;

FIG. 3B is a schematic graph illustrating the variation in reflectivitywith polar direction for reflected light rays in FIG. 1A and FIG. 2A ina privacy mode of operation; FIG. 3C is a schematic graph illustratingthe variation of output luminance with polar direction for transmittedlight rays in FIG. 1A and FIG. 2B in a public mode of operation; andFIG. 3D is a schematic graph illustrating the variation in reflectivitywith polar direction for reflected light rays in FIG. 1A and FIG. 2B ina public mode of operation comprising the embodiments illustrated inTABLE 1.

TABLE 1 Passive polar control retarder 330A & 330B Active LC polarcontrol retarder 301 Mode Type Δn.d/nm Alignment layers Pretilt/degΔn.d/nm Δε Voltage/V Public Crossed A +500 @ 45°  Homogeneous 2 750 13.210 Privacy +500 @ 135° Homogeneous 2 2.3

In the present embodiment, the switchable liquid crystal retarder 301comprises two surface alignment layers (not shown) disposed adjacent tothe layer 314 of liquid crystal material 414 and on opposite sidesthereof. Each alignment layer is arranged to provide homogeneousalignment in the adjacent liquid crystal material 414. The layer 314 ofliquid crystal material 414 of the switchable liquid crystal retarder301 comprises a liquid crystal material 414 with a positive dielectricanisotropy. The layer of liquid crystal material 414 has a retardancefor light of a wavelength of 550 nm in a range from 500 nm to 900 nm,preferably in a range from 600 nm to 850 nm and most preferably in arange from 700 nm to 800 nm. The at least one retarder 330 furthercomprises a pair of passive retarders 308A, 308B which have optical axesin the plane of the retarders that are crossed, each passive retarder ofthe pair of passive retarders having a retardance for light of awavelength of 550 nm in a range from 300 nm to 800 nm, preferably in arange from 350 nm to 650 nm and most preferably in a range from 450 nmto 550 nm.

In the present embodiments, ‘crossed’ refers to an angle ofsubstantially 90° between the optical axes of the two retarders in theplane of the retarders. The passive retarders may be provided usingstretched films to advantageously achieve low cost and high uniformity.To reduce cost of retarder materials, it is desirable to providematerials with some variation of retarder orientation due to stretchingerrors during film manufacture for example.

Thus, in a public mode of operation as illustrated in FIGS. 3C and 3D,substantially a high luminance output and low reflectivity is providedover a wide viewing freedom. In comparison, as illustrated in FIGS. 3Aand 3B the luminance is increased and reflectivity is reduced forobservers located in off-axis viewing positions.

Switchable directional display apparatuses for use in privacy displayfor example and comprising plural retarders arranged between a displaypolariser and an additional polariser are described further in U.S. Pat.No. 10,126,575 and in U.S. patent application Ser. No. 16/131,419 titled“Optical stack for switchable directional display”, filed Sep. 14, 2018,both of which are herein incorporated by reference in their entireties.Directional display apparatuses further comprising reflective polarisersarranged between the display polariser and retarders are described inU.S. Patent Publ. No. 2018-0329245, which is herein incorporated byreference in its entirety. Directional display polarisers comprisingpassive retarders arranged between a display polariser and an additionalpolariser are described in U.S. Patent Publ. No. 2018-0321553, which isherein incorporated by reference in its entirety.

Advantageously a switchable privacy display may be provided with a largepolar region in which high visual security level is provided in aprivacy mode of operation and a large polar region in which high imagevisibility is provided in a public mode of operation. Touch electrodearrays are provided at low cost and with minimal additional thickness.High image contrast may be provided in privacy mode for the head ondisplay user and for multiple display users in public mode.

The operation of the privacy mode of the display of FIG. 1A and FIGS.2A-B will now be described further.

FIG. 4A is a schematic diagram illustrating in front perspective view,observation of reflected ambient light from interface surfaces of adisplay operating in public mode. Some light rays 404 may be reflectedby the front surface of the additional polariser 318, or cover glass andother surfaces of the display. Typically, such reflectivity may be 4%for a bonded optical stack at normal incidence and approximately 5% fora bonded optical stack for 45 degrees incidence, due to Fresnelreflections at the air-polariser or air-glass interface. Thus a lowluminance reflected image 605 of source 604 may be observed by thesnooper on the front of the display 100. Further dark image data 601 andbright image data 603 is seen with high luminance by observer 47, suchthat image data can be clearly observed. Display output light 400provides light to both observers 45, 47 so both can see image data andadvantageously public mode is provided.

FIG. 4B is a schematic diagram illustrating in front perspective viewobservation of reflected ambient light for the display of FIG. 1Aoperating in privacy mode. By way of comparison with FIG. 4A,substantially higher reflected luminance is observable from reflection606 of source 604 as polarised light off-axis is reflected fromreflective polariser 302.

Further image luminance in region 27 occupied by snooper 47 issubstantially reduced compared to light to observer 45 in region 26.Image visibility is thus compromised for snooper 47 and a private imageis advantageously provided.

The shape and distribution of the reflected image 606 is determined bythe spatial distribution of ambient light source 604 but may be furtherdetermined by diffusion layers, particularly at the output surface ofthe additional polariser 318.

It may further be desirable to provide controllable display illuminationin an automotive vehicle.

FIG. 4C is a schematic diagram illustrating in side view an automotivevehicle with a switchable directional display 100 arranged within thevehicle cabin 602 of an automotive vehicle 600 for both entertainmentand sharing modes of operation. Light cone 610 (for example representingthe cone of light within which the luminance is greater than 50% of thepeak luminance) may be provided by the luminance distribution of thedisplay 100 in the elevation direction and is not switchable. Furtherdisplay reflectivity may be increased compared to head-on reflectivityoutside this light cone 610.

FIG. 4D is a schematic diagram illustrating in top view an automotivevehicle with a switchable directional display 100 arranged within thevehicle cabin 602 in an entertainment mode of operation and operates ina similar manner to a privacy display. Light cone 612 is provided with anarrow angular range such that passenger 606 may see the display 100whereas driver 604 may not see an image on the display 100 as aconsequence of reduced luminance and increased reflectivity.Advantageously entertainment images may be displayed to the passenger606 without distraction to the driver 604.

FIG. 4E is a schematic diagram illustrating in top view an automotivevehicle with a switchable directional display 100 arranged within thevehicle cabin 602 in a sharing mode of operation. Light cone 614 isprovided with a wide angular range such that all occupants may perceivean image on the display 100, for example when the display is not inmotion or when non-distracting images are provided.

Further stray light in night-time operation may be reduced, such thatdistracting internal light in the vehicle cabin is reduced, and drivervisibility of objects in the vicinity of the vehicle is advantageouslyimproved. The displays of FIGS. 4A-E may advantageously be provided withtouch sensing capability with high sensitivity and with high imagequality.

The operation of touch input structures will now be further described.

FIG. 5 is a schematic diagram illustrating in side view the touch inputdisplay device of FIG. 1A. Features of the embodiment of FIG. 5 notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

In a touch mode of operation, the signal applied to and measured fromthe touch electrode arrays 500, 502 provides a projected capacitivefield 570 with effective capacitance 571. Finger 25 provides somedistortion of the field lines 572, and modifies the capacitance that ismeasured from the touch electrode arrays 500, 502.

SLM 48 is provided with pixel drive electrodes 202. It would bedesirable that the signal provided to the pixels of the SLM 48 is notinterfered with by the signals for the touch control system and that thesensitivity of the touch control system is not interfered with by thesignal provided to the SLM 48. In the present embodiments, theelectrodes 413, 415 provide shielding between the pixel drive electrodes202 and the touch sensing system. The electrical signal shieldingdescribed above increase the signal to noise ratio of the touch signaldetection. Advantageously the touch sensitivity is increased and imagestability is not degraded. Further the present embodiments do not needto use touch sensing methods at inter-pixel locations in the SLM 48 sothat the aperture ratio of the pixels is increased. Advantageously theincreased aperture ration allows more light transmission through thedisplay panel. Further advantageously the resolution of the display isnot reduced by the integration of touch sensing circuitry at the pixellocations of the SLM 48.

Some known displays use the interaction of the light emission from thedisplay with the finger or touch stylus. When the output angle of lightis different in the public and private modes, the sensitivity andperformance of the touch system may vary according to the display mode.In the embodiments described where the touch electrodes 500, 502 are notlocated at the pixel plane of SLM 48 and the operation and sensitivityof the touch sensing is independent of whether the display is operatingin public or privacy modes.

Arrangements of touch electrode arrays 500, 502 will now be described.

FIG. 6A is a schematic diagram illustrating in perspective front viewelectrodes and control system 400, 450, 350, 250 for a touch inputdisplay device. Features of the embodiment of FIG. 6A not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

The touch electrode arrays 500, 502 are arranged on opposite sides of adielectric layer 504. System controller 400 enables the voltage driver350 and touch controller 450 to be synchronised so that driving andmeasuring the signal from the touch controller may take place during atime in which the drive voltage on the switchable liquid crystalretarder is constant, for example zero. This enables the signal to noiseratio (SNR) of the measuring process to be improved which increases thetouch sensitivity and immunity to electrical interference. The variationin capacitance to be measured or detected may be of the order of femtoFarads. The measurement circuit may comprise a capacitance to voltageconverter circuit and may further comprise analog signal processingcircuits. Alternatively or additionally a capacitance to digital circuitcan be used and further comprise digital signal processing functions.The measurement circuit may be gated with the waveform 436 to improvethe SNR. The measurement circuit may include frequency filtering todiscriminate in favour of the frequency band of the touch panel signaldriving and discriminate against other frequencies, improving the SNR.The electrodes 415 and 413 may screen the high frequency driving signalsto the SLM 48 from the touch electrode arrays 500, 502 so that the SNRof the measuring process may be improved without the need to synchroniseto the vertical blanking interval (VBI) of SLM 48. However systemcontroller 400 may also synchronise the touch controller 450 and the SLM48 for example so that the driving and measuring of the signal for thetouch controller occurs during the VBI of the SLM 48 addressing whichfurther improves SNR of the touch measurement.

The drive voltage that the control system 400 is arranged to apply tothe switchable retarder control electrodes 413, 415 is synchronised withrespect to the addressing of the SLM 48.

In operation, it is desirable to provide (i) driving of image data (ii)control of switchable liquid crystal layer for both wide and privacymodes of operation and (iii) touch input.

Some types of display provide in-cell touch, that is electrodes 202 mayfurther provide touch input function. By way of comparison with thepresent embodiments if in-cell touch projected field lines 570 were tobe provided by some of the electrodes 202 of the SLM 48, the electrodes413, 415 of the liquid crystal retarder may shield the projected fieldfrom such in-cell electrodes and may reduce the signal to noise ratio ofthe measurement of the signal from the touch electrode arrays 202. Suchin-cell touch electrode arrays 202 may thus be ineffective for provisionof a touch function in the presence of switchable liquid crystalretarder 314. In operation, the electrodes 413, 415 of the liquidcrystal retarder may provide further electric field lines such that theprojected field 570 from touch electrode arrays 500, 502 may reduce thesignal to noise ratio of the measurement of the signal from the touchelectrode arrays 500, 502. It would be desirable to provide a highsignal to noise ratio for the touch control system comprising touchdrivers 452, 454 and touch control system 450.

It would be desirable to achieve touch input without shielding of thetouch signals by the electrodes 413, 415 of the switchable liquidcrystal layer 314.

FIG. 6B is a schematic diagram illustrating in perspective front view afurther electrode arrangement for a touch input display device. Incomparison to the arrangement of FIG. 6A, the touch electrode array is asingle array 503 that is arranged on a single surface of thecompensation retarder 330. Advantageously a simpler structure may beprovided. The touch electrode array 503 is formed on a surface of one ofthe at least one passive polar control retarders 330.

FIG. 6C is a schematic diagram illustrating in perspective front viewthe electrode arrays 500, 502 of a further arrangement for a touch inputdisplay device. In comparison to FIG. 6B the electrodes on the samesurface are insulated from each other by small insulating bridges (notshown) at the cross overs between electrode arrays 500, 502. Thisarrangement increases the fringe fields between the sets of electrodesand the SNR of the detection and measurement is therefore increased.

FIG. 6D is a schematic diagram illustrating in cross sectional side viewan arrangement of cross section A-A′ in FIG. 6C wherein insulatingbridges are replaced by a continuous dielectric layer 504. Features ofthe embodiments of FIGS. 6C-D not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

A control circuit for driving and measuring the signal from a touchsensor will now be described.

FIG. 7 is a schematic diagram illustrating an equivalent circuit forcontrol of a touch input device. The touch panel system may generate avoltage Vsource with respect to a reference potential Vref_1, which maybe a complex waveform as will be described later. Vsource is applied toa first array of the touch panel electrodes as explained below. Thefirst array of electrodes forms a spatial matrix of capacitors, forexample Cmatrix, with elements of the second array of electrodes. Thesecond array of electrodes may be on the same side of a substrate, onopposite sides of a substrate or on two separate substrates. When thepulse Vsource is applied to the first array of electrodes, a signal canbe detected at the second array of electrodes for example voltageVdetect. The voltage Vsource and detection voltage Vdetect may besequentially scanned or connected to one or more of the electrodescomprising the array of first and second electrodes respectively inorder to measure a spatial array of capacitances across the displaysurface. When the panel surface is touched, the presence of a fingerdistorts the electric field in its proximity and this can be detected asa change in capacitance and may be measured as a change in the voltageVdetect at each of the associated matrix of capacitances. This change incapacitance is illustrated by Cfinger. For equipment plugged in to mainspower, Vref_1 and Vref_2 may be considered to be at ground potential.For battery powered equipment, Vref_1 may be considered as a floatingpotential.

In the diagrams of this specification, one finger 25 is shown forclarity, however the touch panels of the present embodiments are capableof resolving multiple touches from 1 or more fingers. The finger (orfingers) produces a change in the dielectric applicable to one or moreelements of Cmatrix which may be detected as a change in capacitance atVdetect.

The array of second electrodes may comprise different shaped electrodes.In particular the shape may be designed so that the detection circuitmay more easily differentiate between the wanted signal voltage changesto Vdetect caused by the presence of a finger and for example injectednoise voltages picked up by the finger acting as an antenna.

FIG. 8 is a schematic diagram illustrating in perspective front viewdriving of a switchable liquid crystal retarder with voltage waveforms430, 432 driven by means of connecting wires 427, 429 to electrodes 413,415 of the switchable retarder containing liquid crystal layer 314comprising liquid crystal material 414. Features of the embodiment ofFIG. 8 not discussed in further detail may be assumed to correspond tothe features with equivalent reference numerals as discussed above,including any potential variations in the features.

Driving waveforms for the switchable liquid crystal retarder and touchcontroller 450 will now be described.

FIG. 9A is a schematic graph illustrating driving waveforms for drivingof a switchable liquid crystal retarder comprising a first voltagewaveform 430 provided to electrode 413 that is zero volts and a secondvoltage waveform 432 provided to electrode 415 that is an alternatingvoltage waveform, when a dual rail power supply is provided. The voltagewaveform 430 may be at ground potential or at a reference potential inbattery powered equipment. The voltage waveform 432 may have a firstaddressing positive voltage phase provided with positive maximum +V1;and a second addressing negative voltage phase with a negative minimumvoltage −V1. Using this arrangement, the switchable liquid crystalretarder may be driven by a single drive amplifier. Advantageously thedrive circuit complexity is reduced.

FIG. 9B is a schematic graph illustrating alternative driving voltagewaveforms 430, 432 for driving of a switchable liquid crystal retarderwhen only a single rail power supply is provided with voltage rail V1.Features of the embodiment of FIG. 9B not discussed in further detailmay be assumed to correspond to the features with equivalent referencenumerals as discussed above, including any potential variations in thefeatures.

The waveforms 430, 432 are shown driven in anti-phase. Using thisarrangement, the switchable liquid crystal retarder may be driven by twodrive amplifiers. Advantageously the power supply can be a single railtype and therefore complexity and cost is reduced.

FIG. 10 is a schematic graph illustrating a resultant voltage waveform434 provided across the liquid crystal retarder 301 for the drivingwaveforms of FIGS. 9A-B, and the waveform 436 for the control signal forthe touch controller 450. Features of the embodiment of FIG. 10 notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

The waveform 434 of the drive voltage comprises an addressing sequencecomprising a first addressing positive voltage phase 431 with a positivemaximum voltage level 435; and a second addressing negative voltagephase 433 with a negative minimum voltage level 437. In the waveform 434for the drive voltage across the layer 314 of liquid crystal material ofFIG. 10, the voltage transitions are shown as essentially instantaneous.In practice, some transition time is present. The drive voltage acrossthe layer 314 of liquid crystal material has a waveform 434 includingperiods 451, 453 where the drive voltage is constant, and the controlsystem 400 is arranged to address the at least one touch electrode array500, 502 during at least one of the periods 451, 453 where the drivevoltage is constant. Thus the waveform 436 is provided during theperiods 451. In another embodiment, the waveform 436 may be providedduring the periods 453.

The arithmetic average of the waveform 434 of the drive voltage is zero.In other words, the arithmetic average potential experienced by theswitchable liquid crystal layer 314 between electrodes 413, 415 is zero.Advantageously the liquid crystal material 414 in the layer 314 of theliquid crystal retarder is DC balanced. Charge migration effects areminimised and cell lifetime and performance is optimised.

FIG. 10 further illustrates the touch control waveform 436 applied tothe touch controller 450. When the touch control waveform 436 is in afirst low state, no signal is provided to the controller 450 and notouch sensing is provided. When the touch control waveform 436 is in asecond high state, a signal is provided to the controller 450, andsignals are applied to and measured from touch electrode arrays 500, 502by means of touch drivers 452, 454.

Thus the signal applied to and measured from the touch electrode arrays500, 502 is provided when the drive voltage of the resultant voltagewaveform 434 is at a constant level.

The active state of the touch control waveform 436 is provided for aperiod that is less than or equal to the length of a constant voltagelevel of waveform 434, for example period 431. Further the signalapplied to and measured from the touch electrode arrays 500, 502 isprovided when the drive voltage of the voltage waveform 434 is at thesame constant level 435 each time the signal is applied to and measuredin waveform 434.

The signal to noise ratio of detection of touched position may beincreased because there is reduced variation of the fringe fieldexperienced by the touch electrode arrays 500, 502 attributed tointerference from a changing electric field on the switchable liquidcrystal retarder electrodes 413, 415 and therefore the contribution tothe variation in capacitance from the proximity of the finger is easierto discriminate. Advantageously the sensitivity of the touch detectionmay be increased and accuracy improved.

It would be desirable to increase signal to noise ratio of the touchmeasurement system. Further voltage waveforms 434 and correspondingtouch control waveforms 436 will now be described.

FIGS. 11A-D are schematic graphs each illustrating a resultant voltagewaveform 434 provided across the liquid crystal retarder layer 314 andcorresponding timing of a touch control signal 436 for application toand measurement from the touch electrode arrays 500, 502. Features ofthe embodiments of FIGS. 11A-D not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

Thus the waveform 434 of the drive voltage in the first phase comprisesat least one positive voltage level and a zero voltage level; and thewaveform of the drive voltage in the second phase comprises at least onenegative voltage level and a zero voltage level.

In FIG. 11A, the drive voltage across the layer 314 of liquid crystalmaterial 414 has a waveform 434 including periods 451, 453, 455 wherethe drive voltage is constant, and the control system 400 is arranged toaddress the at least one touch electrode array 500, 502 during at leastone of the periods 451, 455 where the drive voltage is constant. Thewaveform 434 of the drive voltage includes a positive addressing phase431 including at least one pulse 461 of positive polarity with level V2and a negative addressing phase 433 including at least one pulse 463 ofnegative polarity with level −V2.

The waveform 436 is provided during the periods 451, 455. The drivevoltage has a waveform 434 including periods 451, 453, 455 where thedrive voltage is constant but of respectively different levels +V2, 0,−V2 and the control system 400 is arranged to address the at least onetouch electrode array 500, 502 during at least one of the periods 451,455 where the drive voltage is constant and at the same level that iszero volts.

In other words, the waveform 434 of the drive voltage includes apositive addressing phase 431 including at least one pulse 461 ofpositive polarity and at least one additional period 465 and a negativeaddressing phase 433 including at least one pulse 463 of negativepolarity and at least one additional period 467, the at least oneadditional period 465 of the positive addressing phase 431 and the atleast one additional period 467 of the negative addressing phase 433being said periods 451, 455 where the drive voltage is constant and hasa level intermediate the maximum level of the at least one pulse 461 ofpositive polarity and the minimum level of the at least one pulse 463 ofnegative polarity. The at least one additional period 465 of thepositive addressing phase 431 and the at least one additional period 467of the negative addressing phase 433 have a level of zero volts.

The drive voltage has a waveform 434 having a root mean square valuethat provides a constant liquid crystal optical alignment state of theliquid crystal retarder 301 and having arithmetic average of zero.

FIG. 11A illustrates that the touch control signal is applied to andmeasured from the touch electrode arrays is provided during time that isless than or equal to Ts when the drive voltage waveform 434 is at aconstant level and when the voltage waveform 434 is zero volts. Thevoltage drive waveform 434 may be non-zero at other times for exampleshown during the time Td.

In comparison to the arrangement of FIG. 10, the signal to noise ratioof detection of touched position may be increased because there isreduced absolute level of the fringe field experienced by the touchelectrode arrays 500, 502 attributed to interference from the electricfield on the switchable liquid crystal retarder electrodes 413, 415 andtherefore the contribution to the variation in capacitance from theproximity of the finger 25 is easier to discriminate. Advantageously thesensitivity of the touch detection may be increased and accuracyimproved.

High frequency detection reduces the perceived lag in the recordedposition of finger 25. The entire slot Ts or a portion within Ts may beused for the signal being applied to and measured from the touchelectrode array.

Alternatively some of the zero voltage time slots in the waveform 434may be unused for touch measurement, that is some of the pulses of thewaveform 436 may be removed. This achieves a lower processing load onthe controller 450 of the measurement of the touch signal while allowingthe operational frequency of the switchable liquid crystal retarder tobe set to a higher level. Advantageously the operating frequency of theswitchable liquid crystal retarder may be set freely to suit thematerial and optical system.

It may be desirable to increase the length of time for which touchmeasurement is provided.

As shown in FIG. 11B, the zero voltage times of waveform 434 may beincreased. To maintain the desirable liquid crystal alignment, thenegative minimum voltage −V3 and positive maximum voltage +V3 may havegreater magnitude than V2 shown in FIG. 11A. The same overall root meansquare (RMS) drive to the switchable liquid crystal layer 314 may beprovided. Increased detection time enables more electrodes to bemeasured and this may increase the accuracy of the touch positionmeasurement. The directional output may be advantageously maintained,and the detection time increased such that advantageously sensitivity,response time and accuracy is achieved.

It may be desirable to reduce high frequency temporal signals in theelectric field from the switchable liquid crystal retarder electrodes413, 415.

As illustrated in FIG. 11C, the waveform of the drive voltage can beother than a square wave. Using for example a waveform 434 with atrapezoidal waveform profile 439 reduces the high frequency Fouriercomponents and reduces the electrical interference from the driving ofthe liquid crystal retarder 301. Advantageously signal to noise ratio ofthe touch measurement may be improved.

By way of comparison with FIG. 11A, FIG. 11D illustrates that the peaksof the at least one pulse 461 of positive polarity and the peaks of theat least one pulse 463 of negative polarity are the said periods 451,453 where the drive voltage is constant.

A method of controlling a touch input display device 100 thus comprises:a SLM 48 arranged to output light 400; a display polariser 218 arrangedon the output side of the SLM 48; an additional polariser 318 arrangedon the output side of the display polariser 218; a switchable liquidcrystal retarder 301 comprising a layer 314 of liquid crystal material414 arranged between the display polariser 218 and the additionalpolariser 318; at least one passive polar control retarder 330 arrangedbetween the switchable liquid crystal retarder 301 and the additionalpolariser 318; switchable retarder control electrodes 413, 415 arrangedto apply a voltage for controlling the switchable liquid crystalretarder 301; and at least one touch electrode array 500, 502 arrangedin at least one layer on the output side of the switchable retardercontrol electrodes 413, 415, wherein the method comprises: applying adrive voltage to the switchable retarder control electrodes 413, 415 forcontrolling the switchable liquid crystal retarder 301, wherein thedrive voltage has a waveform 434 including periods 451, 453, 455 wherethe drive voltage is constant; and addressing the at least one touchelectrode array 413, 415 for capacitive touch sensing during at leastone of the periods 451, 453, 455 where the drive voltage is constant.

It may be desirable to further increase the frequency of themeasurements of the touch position.

FIG. 12A is a schematic graph illustrating two further example drivingvoltage waveforms 430, 432; and FIG. 12B is a schematic graphillustrating a resultant voltage waveform 434. Features of theembodiments of FIGS. 12A-B not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

Each of the first and second addressing phases 431, 433 comprises adrive voltage level 441 intermediate the positive maximum voltage 435and negative minimum voltage 437. The intermediate voltage level 441 iszero volts. In other words, the voltage waveform 434 in the first phase431 comprises at least one positive voltage level 435 and a zero voltagelevel 441; and the resultant waveform 434 of the drive voltage in thesecond phase 433 comprises at least one negative voltage level 437 and azero voltage level 441.

The root mean square (RMS) value of the waveform 434 of the drivevoltage is arranged to provide a constant liquid crystal opticalalignment state of the liquid crystal retarder and the arithmeticaverage of the waveform 434 of the drive voltage is zero.

As illustrated an increased density or frequency of time slots Ts inwhich the signal applied to and measured from the touch electrode arraysmay be provided. Increasing the density of the measurement time slots Tscan reduce the latency of the touch signal measurement which improvesthe reliability of the touch interaction when the finger 25 or fingersare moving. Providing the signals applied to and measured from the touchelectrode arrays 500, 502 while the voltage on the switchable liquidcrystal retarder is at the same constant value improves the signal tonoise ratio of the touch measurement system and advantageously improvesreliability.

In some circumstances it would be desirable to make the touch signalmeasurements at a voltage other than ground.

FIGS. 13A-B are schematic graphs illustrating resultant voltagewaveforms provided across the liquid crystal retarder with three andfour drive voltage levels respectively. Features of the embodiments ofFIGS. 13A-B not discussed in further detail may be assumed to correspondto the features with equivalent reference numerals as discussed above,including any potential variations in the features.

The at least one additional period 465 of the positive addressing phase431 and the at least one additional period 467 of the negativeaddressing phase 433 have a level V1 of non-zero magnitude.

In FIG. 13A the voltage waveform 434 in the first phase 431 comprises afirst positive voltage level 435 and a second voltage level 442; and theresultant waveform 434 of the drive voltage in the second phase 433comprises at least one negative voltage level 437 and the second voltagelevel 442.

In FIG. 13B the waveform 434 of the drive voltage in the first phase 431comprises more than one positive voltage level 435, 443; and thewaveform 434 of the drive voltage in the second phase 433 comprises morethan one negative voltage level 444, 437.

The measurement of the touch signals may be done while the resultantvoltage waveform 434 is away from ground in case the ground signal has alot of high frequency electrical noise. Advantageously the reliabilityof the touch signal detection may be improved.

FIG. 14 is a schematic graph illustrating a resultant voltage waveform434 provided across the liquid crystal retarder, corresponding timing ofa control signal waveform 436 for application to and measurement fromthe touch electrode arrays 500, 502, and synchronisation with thevertical blanking interval (VBI) of the SLM 48. Features of theembodiment of FIG. 14 not discussed in further detail may be assumed tocorrespond to the features with equivalent reference numerals asdiscussed above, including any potential variations in the features.

In comparison to the two-phase addressing waveforms 434 of otherembodiments herein, the voltage waveform 434 comprises a thirdaddressing phase 425 comprising an intermediate drive voltage level 446intermediate the positive maximum voltage 435 and negative minimumvoltage 437. The intermediate voltage level 446 is illustrated as zero.

The control system 400 is arranged to address the SLM 48 using anaddressing scheme including a vertical blanking interval VBI, and thecontrol system 400 being arranged to address the at least one touchelectrode array 500, 502 during the vertical blanking interval VBI.

Thus the waveform 436 applied to the switchable liquid crystal retarderis synchronised with respect to the addressing of the SLM 48. Theaddressing waveform 438 of the SLM 48 comprises a vertical blankinginterval (VBI) and the waveform 436 applied to and measured from thetouch electrode arrays 500, 502 is provided during the vertical blankinginterval (VBI). Advantageously the signal to noise ratio of the touchdetection may be improved because there is reduced interference from thehigh frequency signals that comprise the data addressing of the SLM 48.

When the position of the switchable liquid crystal retarder is betweenthe SLM 48 and the touch electrode arrays then the electrodes of theswitchable liquid crystal retarder can substantially shield theelectrical noise effect of the high frequency SLM data phase 438 fromthe touch detection circuit so that synchronising to the SLM may not beprovided. Synchronising to the VBI of the SLM 48 reduces the frequencyof the positional updates from the touch electrode system and thereforeincreases the position lag error for a moving finger. This isparticularly an issue when the addressing frequency of the SLM isreduced below say 60 Hz, for example to save power.

It may be desirable to provide a touch measurement update rate that isdifferent to the addressing of the SLM 48, for example for high speedmovement of finger 25.

FIG. 15 is a schematic graph illustrating a resultant voltage waveformprovided 434 across the liquid crystal retarder, corresponding timing ofa control signal waveform 436 for application to and measurement fromthe touch electrode arrays 500, 502 asynchronously with the drivingwaveform 438 of the SLM 48. Features of the embodiment of FIG. 15 notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features.

Advantageously increased response speed and reduced lag may be providedby the touch system. In addition, the driving signal to the SLM 48 canbe operated independently of the touch panel and be provided by separatesuppliers without the need for their electrical integration. Theshielding of the SLM 48 electrical noise from the touch electrode arrays500 means that the and signal to noise ratio may be maintained withoutlimiting the touch panel update frequency to the VBI periods of the SLM48 addressing and allowing these components to be operated independentlywithout synchronisation. In particular the touch panel control andmeasurement signals can be independent of and compatible with variableaddressing refresh rates of the SLM 48, for example as used in“Freesync™” technology compatible SLMs.

Other structures of switchable directional displays comprising touchelectrode arrays will now be described

FIG. 16A is a schematic diagram illustrating in side view a touch inputdisplay device wherein the dielectric layer 504 is provided by a pair ofcrossed A-plates; FIG. 16B is a schematic diagram illustrating in sideview a touch input display device wherein the dielectric layer isprovided by a pair of crossed A-plates 330A, 330B. Thus the dielectriclayer 504 comprises at least one passive polar control retarder.Features of the embodiments of FIGS. 16A-B not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

The display device 100 comprises more than one passive polar controlretarder 330A, 330B and said at least one dielectric layer 504 comprisesall the passive polar control retarders 330A, 330B. The touch electrodearray comprises a pair of touch electrode arrays 500, 502 formed onouter surfaces of respective ones of the pair of passive uniaxialretarders 330A, and said at least one dielectric layer 504 comprises thepair of passive uniaxial retarders 330A, 330B.

Advantageously crossed A-plates retarders 330A, 330B may achieve widefield of view for high visual security levels. Electrodes mayconveniently be provided on one side of the A-plate retarders 330A, 330Bin a roll to roll fabrication method with low cost. The retarders 330A,330B may be attached by solvent bonding, to reduce thickness andcomplexity and increase robustness to environmental and mechanicalstress.

FIGS. 16A-B further illustrate that the reflective polariser 302 may beomitted to provide a display with off-axis luminance control. Off-axisreflectivity is reduced for arrangements in which side reflections areconsidered undesirable. Advantageously thickness and cost may bereduced.

FIG. 16C is a schematic diagram illustrating in side view a touch inputdisplay device wherein the dielectric layer is provided by one of a pairof crossed A-plate passive polar control retarder 330A. Thus thedielectric layer 504 comprises at least one passive polar controlretarder. Features of the embodiment of FIG. 16C not discussed infurther detail may be assumed to correspond to the features withequivalent reference numerals as discussed above, including anypotential variations in the features.

The at least one passive retarder comprises a pair of passive uniaxialretarders 330A, 330B having optical axes in the plane of the passiveuniaxial retarders that are crossed. Said at least one dielectric layer504 comprises the passive polar control retarder 330A wherein thedisplay device 100 comprises two passive polar control retarders 330A,330B.

In comparison to the arrangements of FIG. 1A and FIG. 2A, the dielectriclayer 504 comprises the pair of crossed A-plate passive polar controlretarders 330A, 330B. The A-plates may be bonded in contact, for exampleby solvent bonding where a low thickness structure is advantageouslyprovided. Advantageously thickness may be reduced. In comparison to thearrangement of FIG. 16B, the electrode arrays 500, 502 are formed on asingle substrate that may reduce fabrication cost as only a singleelement is provided with electrodes. Further the dielectric thickness isreduced that may improve operating characteristics for touch screencapacitive sensing. Advantageously at least one of the electrode arrays500 may be protected by the other of the passive polar control retarders330B.

It may be desirable to provide compensation retarders 330 that are notA-plates.

FIG. 17 is a schematic diagram illustrating in a perspective side view atouch input display device wherein the dielectric layer is providedbetween a pair of C-plates 330A, 330B, that is a pair of passiveuniaxial retarders each having its optical axis perpendicular to theplane of the retarder. Features of the embodiment of FIG. 17 notdiscussed in further detail may be assumed to correspond to the featureswith equivalent reference numerals as discussed above, including anypotential variations in the features. The pair of retarders 330A, 330Bcomprise a pair of passive uniaxial retarders each having its opticalaxis perpendicular to the plane of the retarder. Dielectric material 507may be provided in the dielectric layer 504 between the electrode arrays500, 502 and may be an adhesive material for example.

In comparison to FIG. 16B, the polar region for high image visibility ofFIGS. 3A-3D may be improved, for example to increase viewing freedom inthe public mode of operation. Further the material or materialsprocessing of the C-plates may be different to that of the A-plates ofFIG. 2A, and may provide different adhesion of transparent electrodessuch as ITO. Further the electrode orientations are not desirablyaligned to the stretch direction in the plane of retarder, reducing costand complexity.

FIG. 18A is a schematic diagram illustrating in a perspective side viewa touch input display device wherein the dielectric layer 504 isprovided by a single C-plate 330 having its optical axis perpendicularto the plane of the retarder; and FIG. 18B is a schematic diagramillustrating in side view the touch input display device of FIG. 18A. Anillustrative embodiment is given in TABLE 2. Features of the embodimentof FIGS. 18A-B not discussed in further detail may be assumed tocorrespond to the features with equivalent reference numerals asdiscussed above, including any potential variations in the features.

TABLE 2 Passive polar control retarder 330 Active LC polar controlretarder 301 Mode Type Δn.d/nm Alignment layers Pretilt/deg Δn.d/nm ΔεVoltage/V Public Negative C −700 Homeotropic 88 810 −4.3 0 PrivacyHomeotropic 88 2.2

The passive polar control retarder 330 comprises a passive uniaxialretarder having an optical axis perpendicular to the plane of thepassive uniaxial retarder 330. The dielectric layer 504 comprises thepassive polar control retarder 330. Touch electrode arrays 500, 502 arearranged on opposite sides of the passive polar control retarder 330.Advantageously the number of films may be reduced, reducing thickness,cost and complexity.

A single passive polar control retarder 330 provides the dielectriclayer 504. Advantageously the thickness, cost and complexity of thedisplay device is reduced. Field of view for high image visibility inpublic mode may be increased and field of view for high visual securitylevel in privacy mode of operation may be increased by use of theC-plate.

It may be desirable to provide reduction of luminance in both lateraland elevation directions.

FIG. 19A is a schematic diagram illustrating in side perspective view anoptical stack of a passive polar control retarders 330A-D comprising twopairs of crossed A-plates; and FIG. 19B is a schematic graphillustrating the variation of output transmission with polar directionfor transmitted light rays in the passive retarder of FIG. 19A,comprising the structure illustrated in TABLE 3. Features of thearrangements of FIGS. 19A-B not discussed in further detail may beassumed to correspond to the features with equivalent reference numeralsas discussed above, including any potential variations in the features.

TABLE 3 Passive polar control retarder 330 Layer Type Out-of-planeangle/° In-plane angle/° Δn.d/nm 330A Positive A 0 45 700 330B 90 330C 0330D 135

The retarder thus comprises a pair of passive polar control retarders330A, 330D which have optical axes in the plane of the retarders thatare crossed. The pair of retarders each comprise plural A-plates havingrespective optical axes aligned at different angles from each other. Thepair of passive polar control retarders 330B, 330C have optical axesthat each extend at 90° and 0°, respectively, with respect to anelectric vector transmission direction that is parallel to the electricvector transmission 211 of the display polariser 210.

The pair of passive polar control retarders 330A, 330D have optical axesthat extend at 45° and at 135°, respectively, with respect to anelectric vector transmission direction 211 that is parallel to theelectric vector transmission of the display polariser 218 respectively.

The display further comprises an additional pair of passive polarcontrol retarders 330B, 330C disposed between the first-mentioned pairof passive polar control retarders 330A, 330D and which have opticalaxes in the plane of the retarders that are crossed. The additional pairof passive polar control retarders 330B, 330C have optical axes thateach extend at 0° and at 90°, respectively, with respect to an electricvector transmission direction 211, 317 that is parallel to the electricvector transmission of the display polariser 210, 316.

As described for example with reference to FIGS. 16B-C electrode arrays500, 502 may be formed on the surface of one or two of the passive polarcontrol retarders 330A, 330B, 330C, 330D.

The present embodiment provides a transmission profile that has somerotational symmetry. Advantageously a privacy display may be providedwith reduced visibility of image from a wide field of view for lateralor elevated viewing positions of a snooper. Further, such an arrangementmay be used to achieve enhanced privacy operation for landscape andportrait operation of a mobile display. Such an arrangement may beprovided in a vehicle to reduce stray light to off-axis passengers, andalso to reduced light falling on windscreen and other glass surfaces inthe vehicle.

In comparison to the switchable embodiments provided herein theswitchable liquid crystal retarder is omitted. Touch electrode arrays500, 502 are provided to enable touch control of a passive privacydisplay. Advantageously the thickness and cost of the display can bereduced.

Arrangements wherein the touch electrode arrays are formed on or in thetransparent substrates 312, 316 of the switchable liquid crystalretarder will now be described.

FIG. 20 is a schematic diagram illustrating in side view a touch inputdisplay device 100 wherein the dielectric layer 504 between the touchelectrode arrays 500, 502 is provided between a passive polar controlretarder 330 that may be a C-plate or crossed A-plates 330A, 330B andthe output surface of the output transparent support substrate 316 ofthe switchable liquid crystal retarder 301. Features of the embodimentof FIG. 20 not discussed in further detail may be assumed to correspondto the features with equivalent reference numerals as discussed above,including any potential variations in the features.

The touch input display device 100 further comprises between input andoutput transparent support substrates 312, 316, the layer 314 of liquidcrystal material 414 being arranged between the input and outputtransparent support substrates, and the at least one touch electrodearray being arranged on the output side of the output transparentsupport substrate 316. The substrate 316 may have the electrode patternof touch electrode array 502 formed on its light output side and thepassive polar control retarder 330 may have the touch electrode array500 formed on its input side for output light from the SLM 48.Dielectric material 507, that may for example be an inorganic materialsuch a silicon dioxide and/or an adhesive is provided between the touchelectrode arrays 500, 502.

Advantageously a single retarder may be provided with an electrode on asingle surface, reducing thickness, cost and complexity. Furthertransparent electrodes may be conveniently formed on transparentsubstrates 316 during fabrication of the switchable liquid crystalretarder 301.

It may be desirable to provide electrode arrays 500, 502, 415 on onlyone side of the transparent output substrate 316.

FIG. 21A is a schematic diagram illustrating in side view a touch inputdisplay device 100 wherein the dielectric layer 504 between the touchelectrode arrays 500, 502 is provided by the output transparent supportsubstrate 316 and adhesive layer 322. The electrode array 500 is formedon the passive polar control retarder 330 and the electrode 502 isformed on the transparent substrate 316.

Dielectric material 507, that may for example be an inorganic materialsuch a silicon dioxide is provided between the touch electrode array 502and liquid crystal control electrode 415. Electrical interferencebetween the two electrodes 502, 415 may be reduced using the waveformsof the present embodiments described above.

Advantageously electrodes 415, 502 are formed on only one side of thetransparent support substrate 316, reducing complexity of fabrication ofthe substrate 316, and reducing cost.

FIG. 21B is a schematic diagram illustrating in side view a touch inputdisplay device 100 wherein the touch electrode arrays 500, 502 anddielectric layer 504 is provided between one of the liquid crystalcontrol electrode 415 and the output transparent support substrate 316of the switchable liquid crystal retarder. Electrical interferencebetween the electrodes 500, 502, 415 may be reduced using the waveformsof the present embodiments described above. Advantageously all theelectrodes 415, 500, 502 may be formed on one side of a substrate,reducing cost and complexity. In comparison to FIG. 21C below, in thearrangements of FIG. 21A-B the support substrate 316 may be processedwith touch electrode arrays 500, 502 only on one side, advantageouslyreducing complexity and increasing process yield.

FIG. 21C is a schematic diagram illustrating in a perspective side viewa touch input display device 100 that is similar to FIG. 21A, howeverthe electrode array 500 is formed on the output side of the substrate316. Advantageously the electrode structure formed near the liquidcrystal layer is simpler than FIG. 21B. Features of the embodiments ofFIGS. 21A-C not discussed in further detail may be assumed to correspondto the features with equivalent reference numerals as discussed above,including any potential variations in the features.

FIG. 22 is a schematic diagram illustrating in a perspective side view atouch input switchable privacy display device 100 wherein the touchelectrode arrays 500, 502 are arranged between the liquid crystal polarcontrol retarder 301 and additional polariser 318. In comparison toembodiments above, the passive polar control retarder 330 is arrangedbetween the liquid crystal retarder 301 and the display output polariser218. Transparent substrates 370, 372 are provided that have electrodearrays 500, 502 formed on respective surfaces, with dielectric layer 504formed therebetween. The transparent substrates 370, 372 may have lowbirefringence of may have optical axis aligned parallel or orthogonal tothe polariser 318 for example. Electrical interference between theelectrodes 500, 502, 413, 415 may be reduced using the waveforms of thepresent embodiments described above. Features of the embodiment of FIG.22 not discussed in further detail may be assumed to correspond to thefeatures with equivalent reference numerals as discussed above,including any potential variations in the features.

Advantageously passive control retarders 330 that do not have surfaceproperties that are suitable for forming transparent electrodes 500, 502may be provided. Further the electrode structure formed on thetransparent substrate 316 has reduced complexity in comparison to thearrangement of FIGS. 21B-C.

The operation of polar control retarder layers between parallelpolarisers for off-axis illumination will now be described further. Inthe various devices described above, at least one polar control retarderis arranged between the reflective polariser 318 and the additionalpolariser 218 in various different configurations. In each case, the atleast one polar control retarder is configured so that it does notaffect the luminance of light passing through the reflective polariser318, the at least one polar control retarder, and the additionalpolariser 218 along an axis along a normal to the plane of the polarcontrol retarder(s) but it does reduce the luminance of light passingthrough the reflective polariser 318, the at least one polar controlretarder, and the additional polariser 218 along an axis inclined to anormal to the plane of the polar control retarder(s), at least in one ofthe switchable states of the compensated switchable polar control polarcontrol retarder 300. There will now be given a description of thiseffect in more detail, the principles of which may be applied in generalto all of the devices described above.

FIG. 23A is a schematic diagram illustrating in perspective viewillumination of a polar control retarder layer by off-axis light. Polarcontrol retarder 630 may comprise birefringent material, represented byrefractive index ellipsoid 632 with optical axis direction 634 at 0degrees to the x-axis, and have a thickness 631. Features of thearrangements of FIGS. 23A-25E below that are not discussed in furtherdetail may be assumed to correspond to the features with equivalentreference numerals as discussed above, including any potentialvariations in the features.

Normal light rays 636 propagate so that the path length in the materialis the same as the thickness 631. Light rays 637 are in the y-z planehave an increased path length; however the birefringence of the materialis substantially the same as the rays 636. By way of comparison lightrays 638 that are in the x-z plane have an increased path length in thebirefringent material and further the birefringence is different to thenormal ray 636.

The retardance of the polar control retarder 630 is thus dependent onthe angle of incidence of the respective ray, and also the plane ofincidence, that is rays 638 in the x-z will have a retardance differentfrom the normal rays 636 and the rays 637 in the y-z plane.

The interaction of polarized light with the polar control retarder 630will now be described. To distinguish from the first and secondpolarization components during operation in a directional backlight 101,the following explanation will refer to third and fourth polarizationcomponents.

FIG. 23B is a schematic diagram illustrating in perspective viewillumination of a polar control retarder layer by off-axis light of athird linear polarization state at 90 degrees to the x-axis and FIG. 23Cis a schematic diagram illustrating in perspective view illumination ofa polar control retarder layer by off-axis light of a fourth linearpolarization state at 0 degrees to the x-axis. In such arrangements, theincident linear polarization states are aligned to the optical axes ofthe birefringent material, represented by ellipse 632. Consequently, nophase difference between the third and fourth orthogonal polarizationcomponents is provided, and there is no resultant change of thepolarization state of the linearly polarized input for each ray 636,637, 638. Thus, the polar control retarder 630 introduces no phase shiftto polarisation components of light passed by the polariser on the inputside of the polar control retarder 630 along an axis along a normal tothe plane of the polar control retarder 630. Accordingly, the polarcontrol retarder 630 does not affect the luminance of light passingthrough the polar control retarder 630 and polarisers (not shown) oneach side of the polar control retarder 630. Although FIGS. 29A-C relatespecifically to the polar control retarder 630 that is passive, asimilar effect is achieved by the polar control retarders in the devicesdescribed above.

FIG. 23D is a schematic diagram illustrating in perspective viewillumination of a polar control retarder 630 layer by off-axis light ofa linear polarization state at 45 degrees. The linear polarization statemay be resolved into third and fourth polarization components that arerespectively orthogonal and parallel to optical axis 634 direction. Thepolar control retarder thickness 631 and material retardance representedby refractive index ellipsoid 632 may provide a net effect of relativelyshifting the phase of the third and fourth polarization componentsincident thereon in a normal direction represented by ray 636 by half awavelength, for a design wavelength. The design wavelength may forexample be in the range of 500 to 550 nm.

At the design wavelength and for light propagating normally along ray636 then the output polarization may be rotated by 90 degrees to alinear polarization state 640 at −45 degrees. Light propagating alongray 637 may see a phase difference that is similar but not identical tothe phase difference along ray 637 due to the change in thickness, andthus an elliptical polarization state 639 may be output which may have amajor axis similar to the linear polarization axis of the output lightfor ray 636.

By way of contrast, the phase difference for the incident linearpolarization state along ray 638 may be significantly different, inparticular a lower phase difference may be provided. Such phasedifference may provide an output polarization state 644 that issubstantially circular at a given inclination angle 642. Thus, the polarcontrol retarder 630 introduces a phase shift to polarisation componentsof light passed by the polariser on the input side of the polar controlretarder 630 along an axis corresponding to ray 638 that is inclined toa normal to the plane of the polar control retarder 630. Although FIG.29D relates to the polar control retarder 630 that is passive, a similareffect is achieved by the polar control retarders described above, in aswitchable state of the switchable liquid crystal polar control retardercorresponding to the privacy mode.

To illustrate the off-axis behaviour of polar control retarder stacks,the angular luminance control of C-plates 330A, 330B between anadditional polariser 318 and output display polariser 218 will now bedescribed for various off-axis illumination arrangements with referenceto the operation of a C-plate between the parallel polarisers 218, 210will now be described.

FIG. 24A is a schematic diagram illustrating in perspective viewillumination of a C-plate layer by off-axis polarised light with apositive elevation. Incident linear polarisation component 704 isincident onto the birefringent material 632 of the polar controlretarder 560 that is a C-plate with optical axis direction 507 that isperpendicular to the plane of the polar control retarder 560.Polarisation component 704 sees no net phase difference on transmissionthrough the liquid crystal molecule and so the output polarisationcomponent is the same as component 704. Thus a maximum transmission isseen through the polariser 210. Thus the polar control retarder 560having an optical axis 561 perpendicular to the plane of the polarcontrol retarder 560, that is the x-y plane. The polar control retarder560 having an optical axis perpendicular to the plane of the polarcontrol retarder comprises a C-plate.

FIG. 24B is a schematic diagram illustrating in perspective viewillumination of a C-plate layer by off-axis polarised light with anegative lateral angle. As with the arrangement of FIG. 24A,polarisation state 704 sees no net phase difference and is transmittedwith maximum luminance. Thus, the polar control retarder 560 introducesno phase shift to polarisation components of light passed by thepolariser on the input side of the polar control retarder 560 along anaxis along a normal to the plane of the polar control retarder 560.Accordingly, the polar control retarder 560 does not affect theluminance of light passing through the polar control retarder 560 andpolarisers (not shown) on each side of the polar control retarder 560.Although FIGS. 29A-C relate specifically to the polar control retarder560 that is passive, a similar effect is achieved by the polar controlretarders in the devices described above.

FIG. 24C is a schematic diagram illustrating in perspective viewillumination of a C-plate layer by off-axis polarised light with apositive elevation and negative lateral angle. In comparison to thearrangement of FIGS. 24A-B, the polarisation state 704 resolves ontoeigenstates 703, 705 with respect to the birefringent material 632providing a net phase difference on transmission through the polarcontrol retarder 560. The resultant elliptical polarisation component656 is transmitted through polariser 210 with reduced luminance incomparison to the rays illustrated in FIGS. 24A-B.

FIG. 24D is a schematic diagram illustrating in perspective viewillumination of a C-plate layer by off-axis polarised light with apositive elevation and positive lateral angle. In a similar manner toFIG. 24C, the polarisation component 704 is resolved into eigenstates703, 705 that undergo a net phase difference, and ellipticalpolarisation component 660 is provided, which after transmission throughthe polariser reduces the luminance of the respective off-axis ray.Thus, the polar control retarder 560 introduces a phase shift topolarisation components of light passed by the polariser on the inputside of the polar control retarder 560 along an axis that is inclined toa normal to the plane of the polar control retarder 560. Although FIG.29D relates to the polar control retarder 560 that is passive, a similareffect is achieved by the polar control retarders described above, in aswitchable state of the switchable liquid crystal polar control retardercorresponding to the privacy mode.

FIG. 24E is a schematic graph illustrating the variation of outputtransmission with polar direction for transmitted light rays in FIGS.24A-D. Thus, the C-plate may provide luminance reduction in polarquadrants. In combination with switchable liquid crystal layer 314described elsewhere herein, (i) removal of luminance reduction of theC-plate may be provided in a first wide angle state of operation (ii)extended polar region for luminance reduction may be achieved in asecond privacy state of operation.

To illustrate the off-axis behaviour of polar control retarder stacks,the angular luminance control of crossed A-plate passive polar controlretarders 330A, 330B between an additional polariser 318 and outputdisplay polariser 218 will now be described for various off-axisillumination arrangements.

FIG. 25A is a schematic diagram illustrating in perspective viewillumination of crossed A-plate retarder layers by off-axis polarisedlight with a positive elevation. Linear polariser 218 with electricvector transmission direction 219 is used to provide a linearpolarisation state 704 that is parallel to the lateral direction ontofirst A-plate 330A of the crossed A-plate passive polar controlretarders 330A, 330B. The optical axis direction 331A is inclined at +45degrees to the lateral direction. The retardance of the polar controlretarder 330A for the off-axis angle θ₁ in the positive elevationdirection provides a resultant polarisation component 650 that isgenerally elliptical on output. Polarisation component 650 is incidentonto the second A-plate 330B of the crossed A-plate passive polarcontrol retarders 330A, 330B that has an optical axis direction 331Bthat is orthogonal to the optical axis direction 331A of the firstA-plate 330A. In the plane of incidence of FIG. 25A, the retardance ofthe second A-plate 330B for the off-axis angle θ₁ is equal and oppositeto the retardance of the first A-plate 330A. Thus a net zero retardationis provided for the incident polarisation component 704 and the outputpolarisation component is the same as the input polarisation component704.

The output polarisation component is aligned to the electric vectortransmission direction of the additional polariser 318, and thus istransmitted efficiently. Advantageously substantially no losses areprovided for light rays that have zero lateral angle angular componentso that full transmission efficiency is achieved.

FIG. 25B is a schematic diagram illustrating in perspective viewillumination of crossed A-plate retarder layers by off-axis polarisedlight with a negative lateral angle. Thus input polarisation componentis converted by the first A-plate 330A to an intermediate polarisationcomponent 652 that is generally an elliptical polarisation state. Thesecond A-plate 330B again provides an equal and opposite retardation tothe first A-plate so that the output polarisation component is the sameas the input polarisation component 704 and light is efficientlytransmitted through the polariser 318.

Thus the polar control retarder comprises a pair of retarders 330A, 330Bwhich have optical axes in the plane of the retarders 330A, 330B thatare crossed, that is the x-y plane in the present embodiments. The pairof retarders 330A, 330B have optical axes 331A, 331B that each extend at45° with respect to an electric vector transmission direction that isparallel to the electric vector transmission of the polariser 318.

Advantageously substantially no losses are provided for light rays thathave zero elevation angular component so that full transmissionefficiency is achieved.

FIG. 25C is a schematic diagram illustrating in perspective viewillumination of crossed A-plate retarder layers by off-axis polarisedlight with a positive elevation and negative lateral angle. Polarisationcomponent 704 is converted to an elliptical polarisation component 654by first A-plate 330A. A resultant elliptical component 656 is outputfrom the second A-plate 330B. Elliptical component 656 is analysed byinput polariser 318 with reduced luminance in comparison to the inputluminance of the first polarisation component 704.

FIG. 25D is a schematic diagram illustrating in perspective viewillumination of crossed A-plate retarder layers by off-axis polarisedlight with a positive elevation and positive lateral angle. Polarisationcomponents 658 and 660 are provided by first and second A-plate passivepolar control retarders 330A, 330B as net retardance of first and secondretarders does not provide compensation.

Thus luminance is reduced for light rays that have non-zero lateralangle and non-zero elevation components. Advantageously display privacycan be increased for snoopers that are arranged in viewing quadrantswhile luminous efficiency for primary display users is not substantiallyreduced.

FIG. 25E is a schematic graph illustrating the variation of outputtransmission with polar direction for transmitted light rays in FIGS.25A-D. In comparison to the arrangement of FIG. 24E, the area ofluminance reduction is increased for off-axis viewing. However, theswitchable liquid crystal layer 314 may provide reduced uniformity incomparison to the C-plate arrangements for off-axis viewing in the firstpublic mode state of operation.

As may be used herein, the terms “substantially” and “approximately”provide an industry-accepted tolerance for its corresponding term and/orrelativity between items. Such an industry-accepted tolerance rangesfrom zero percent to ten percent and corresponds to, but is not limitedto, component values, angles, et cetera. Such relativity between itemsranges between approximately zero percent to ten percent.

While various embodiments in accordance with the principles disclosedherein have been described above, it should be understood that they havebeen presented by way of example only, and not limitation. Thus, thebreadth and scope of this disclosure should not be limited by any of theabove-described exemplary embodiments, but should be defined only inaccordance with any claims and their equivalents issuing from thisdisclosure. Furthermore, the above advantages and features are providedin described embodiments, but shall not limit the application of suchissued claims to processes and structures accomplishing any or all ofthe above advantages.

Additionally, the section headings herein are provided for consistencywith the suggestions under 37 CFR 1.77 or otherwise to provideorganizational cues. These headings shall not limit or characterize theembodiment(s) set out in any claims that may issue from this disclosure.Specifically and by way of example, although the headings refer to a“Technical Field,” the claims should not be limited by the languagechosen under this heading to describe the so-called field. Further, adescription of a technology in the “Background” is not to be construedas an admission that certain technology is prior art to anyembodiment(s) in this disclosure. Neither is the “Summary” to beconsidered as a characterization of the embodiment(s) set forth inissued claims. Furthermore, any reference in this disclosure to“invention” in the singular should not be used to argue that there isonly a single point of novelty in this disclosure. Multiple embodimentsmay be set forth according to the limitations of the multiple claimsissuing from this disclosure, and such claims accordingly define theembodiment(s), and their equivalents, that are protected thereby. In allinstances, the scope of such claims shall be considered on their ownmerits in light of this disclosure, but should not be constrained by theheadings set forth herein.

The invention claimed is:
 1. A touch input display device comprising: aspatial light modulator (SLM) arranged to output light; a displaypolariser arranged on the output side of the SLM, wherein the displaypolariser is a linear polariser; an additional polariser arranged on theoutput side of the display polariser wherein the additional polariser isa linear polariser; a switchable liquid crystal retarder comprising alayer of liquid crystal material arranged between the display polariserand the additional polariser, wherein the switchable liquid crystalretarder is a polar control retarder that is arranged, in a switchablestate of the switchable liquid crystal retarder, simultaneously tointroduce no net relative phase shift to orthogonal polarisationcomponents of light passed by the display polariser along an axis alonga normal to the plane of the switchable liquid crystal retarder andintroducing a relative phase shift to orthogonal polarisation componentsof light passed by the display polariser along an axis inclined to anormal to the plane of the switchable liquid crystal retarder;switchable retarder control electrodes arranged to apply a voltage forcontrolling the state of the switchable liquid crystal retarder; atleast one passive retarder arranged between the display polariser andthe additional polariser; and a pair of touch electrode arrays arrangedin layers separated by at least one dielectric layer that is not aretarder, the pair of touch electrode arrays and the at least onedielectric layer being arranged between the switchable retarder controlelectrodes and the additional polariser.
 2. A touch input display deviceaccording to claim 1, wherein the at least one passive retarder isarranged between the switchable liquid crystal retarder and theadditional polariser.
 3. A touch input display device according to claim2, wherein the pair of touch electrode arrays and the at least onedielectric layer are arranged between the switchable retarder controlelectrodes and the at least one passive retarder.
 4. A touch inputdisplay device according to claim 2, wherein the at least one passiveretarder is a polar control retarder that simultaneously introduces nonet relative phase shift to orthogonal polarisation components of lightpassed by the display polariser along an axis along a normal to theplane of the switchable liquid crystal retarder and introducing arelative phase shift to orthogonal polarisation components of lightpassed by the display polariser along an axis inclined to a normal tothe plane of the switchable liquid crystal retarder.
 5. A touch inputdisplay device according to claim 2, wherein one of the touch electrodearrays is formed on a surface of the passive retarder in the case thatthe display device comprises one passive retarder or on a surface of oneof the passive retarders in the case that the display device comprisesmore than one passive retarder.
 6. A touch input display deviceaccording to claim 1, wherein the at least one passive retardercomprises a passive uniaxial retarder having an optical axisperpendicular to the plane of the passive uniaxial retarder.
 7. A touchinput display device according claim 1, wherein the at least one passiveretarder comprises a pair of passive uniaxial retarders having opticalaxes in the plane of the passive uniaxial retarders that are crossed. 8.A touch input display device according to claim 2, further comprisinginput and output transparent support substrates, the layer of liquidcrystal material being arranged between the input and output transparentsupport substrates, and the pair of touch electrode arrays and the atleast one dielectric layer being arranged between the output transparentsupport substrate and the additional polariser.
 9. A touch input displaydevice according to claim 8, wherein one of the touch electrode arraysis formed on a surface of the passive retarder in the case that thedisplay device comprises one passive retarder or on a surface of one ofthe passive retarders in the case that the display device comprises morethan one passive retarder.
 10. A touch input display device according toclaim 9, wherein the pair of touch electrode arrays and the at least onedielectric layer are arranged between the output transparent supportsubstrate and the at least one passive retarder.
 11. A touch inputdisplay device according to claim 1, further comprising input and outputtransparent support substrates, the layer of liquid crystal materialbeing arranged between the input and output transparent supportsubstrates, and the pair of touch electrode arrays and the at least onedielectric layer being arranged being arranged between the switchableretarder control electrodes and the output transparent supportsubstrate.
 12. A touch input display device according to claim 1,further comprising input and output transparent support substrates, thelayer of liquid crystal material being arranged between the input andoutput transparent support substrates, wherein said at least onedielectric layer that is not a retarder comprises the output transparentsupport substrate.
 13. A touch input display device according to claim12, wherein the at least one passive retarder is arranged between theoutput transparent support substrate and the additional polariser.
 14. Atouch input display device according to claim 13, wherein one of thetouch electrode arrays is formed on a surface of the passive retarder inthe case that the display device comprises one passive retarder or on asurface of one of the passive retarders in the case that the displaydevice comprises more than one passive retarder.
 15. A touch inputdisplay device according to claim 14, further comprising an adhesivelayer arranged between the output transparent support substrate and saidone of the touch electrode arrays.
 16. A touch input display deviceaccording to claim 12, wherein each of the touch electrode arrays isformed on a surface of the output transparent support substrate.
 17. Atouch input display device according to claim 1, further comprisinginput and output transparent support substrates, the layer of liquidcrystal material being arranged between the input and output transparentsupport substrates, wherein the pair of touch electrode arrays and theat least one dielectric layer are arranged between the outputtransparent support substrate and the additional polariser.
 18. A touchinput display device according to claim 17, wherein the at least onepassive retarder is arranged between the display polariser and the inputtransparent support substrate.
 19. A touch input display deviceaccording to claim 17, comprising a further pair of transparentsubstrates arranged between the output transparent support substrate andthe additional polariser, the pair of touch electrode arrays and the atleast one dielectric layer are arranged between the further pair oftransparent substrates.
 20. A touch input display device according toclaim 19, wherein the at least one passive retarder is arranged betweenthe display polariser and the input transparent support substrate.
 21. Atouch input display device according to claim 1, wherein the switchableretarder control electrodes are arranged on both sides of the layer ofliquid crystal material.
 22. A touch input display device according toclaim 1, further comprising a reflective polariser arranged between thedisplay polariser and the switchable liquid crystal retarder.
 23. Atouch input display device according to claim 1, further comprising acontrol system, wherein the control system is arranged to apply a drivevoltage to the switchable retarder control electrodes for controllingthe switchable liquid crystal retarder, and the control system isarranged to address the at least one touch electrode array forcapacitive touch sensing.
 24. A touch input display device according toclaim 23, wherein the drive voltage has a waveform including periodswhere the drive voltage is constant, and the control system is arrangedto address the at least one touch electrode array during at least one ofthe periods where the drive voltage is constant.
 25. A touch inputdisplay device according to claim 24, wherein the drive voltage has awaveform including periods where the drive voltage is constant but ofrespectively different levels, and the control system is arranged toaddress the at least one touch electrode array during at least one ofthe periods where the drive voltage is constant and at the same level.26. A touch input display device according to claim 25, wherein thewaveform of the drive voltage includes a positive addressing phaseincluding at least one pulse of positive polarity and a negativeaddressing phase including at least one pulse of negative polarity, thepeaks of the at least one pulse of positive polarity and the peaks ofthe at least one pulse of negative polarity being said periods where thedrive voltage is constant.
 27. A touch input display device according toclaim 24, wherein the waveform of the drive voltage includes a positiveaddressing phase including at least one pulse of positive polarity andat least one additional period and a negative addressing phase includingat least one pulse of negative polarity and at least one additionalperiod, the at least one additional period of the positive addressingphase and the at least one additional period of the negative addressingphase being said periods where the drive voltage is constant and has alevel intermediate the maximum level of the at least one pulse ofpositive polarity and the minimum level of the at least one pulse ofnegative polarity.
 28. A touch input display device according to claim27, wherein the at least one additional period of the positiveaddressing phase and the at least one additional period of the negativeaddressing phase have a level of zero volts.
 29. A touch input displaydevice according to claim 27, wherein the at least one additional periodof the positive addressing phase and the at least one additional periodof the negative addressing phase have a level of non-zero magnitude. 30.A touch input display device according to claim 23, wherein the drivevoltage has a waveform having a root mean square value that provides aconstant liquid crystal optical alignment state of the liquid crystalretarder and having arithmetic average of zero.
 31. A touch inputdisplay device according to claim 23, wherein the control system isfurther arranged to address the SLM.
 32. A touch input display deviceaccording to claim 31, wherein the drive voltage that the control systemis arranged to apply to the switchable retarder control electrodes issynchronised with respect to the addressing of the SLM.
 33. A touchinput display device according to claim 31, wherein the control systemis arranged to address the SLM using an addressing scheme including avertical blanking interval, and the control system being arranged toaddress the at least one touch electrode array during the verticalblanking interval.